diff --git a/apps/files/lib/Command/ScanAppData.php b/apps/files/lib/Command/ScanAppData.php
index 23604a82df9b5..ade5e10fe68c2 100644
--- a/apps/files/lib/Command/ScanAppData.php
+++ b/apps/files/lib/Command/ScanAppData.php
@@ -53,6 +53,16 @@ protected function configure(): void {
 		$this->addArgument('folder', InputArgument::OPTIONAL, 'The appdata subfolder to scan', '');
 	}
 
+	protected function getScanner(OutputInterface $output): Scanner {
+		$connection = $this->reconnectToDatabase($output);
+		return new Scanner(
+			null,
+			new ConnectionAdapter($connection),
+			Server::get(IEventDispatcher::class),
+			Server::get(LoggerInterface::class),
+		);
+	}
+
 	protected function scanFiles(OutputInterface $output, string $folder): int {
 		if ($folder === 'preview' || $folder === '') {
 			$this->previewsCounter = $this->previewStorage->scan();
@@ -79,13 +89,7 @@ protected function scanFiles(OutputInterface $output, string $folder): int {
 			}
 		}
 
-		$connection = $this->reconnectToDatabase($output);
-		$scanner = new Scanner(
-			null,
-			new ConnectionAdapter($connection),
-			Server::get(IEventDispatcher::class),
-			Server::get(LoggerInterface::class)
-		);
+		$scanner = $this->getScanner($output);
 
 		# check on each file/folder if there was a user interrupt (ctrl-c) and throw an exception
 		$scanner->listen('\OC\Files\Utils\Scanner', 'scanFile', function ($path) use ($output): void {
@@ -142,6 +146,9 @@ protected function execute(InputInterface $input, OutputInterface $output): int
 
 		$folder = $input->getArgument('folder');
 
+		// Start the timer
+		$this->execTime = -microtime(true);
+
 		$this->initTools();
 
 		$exitCode = $this->scanFiles($output, $folder);
@@ -155,8 +162,6 @@ protected function execute(InputInterface $input, OutputInterface $output): int
 	 * Initialises some useful tools for the Command
 	 */
 	protected function initTools(): void {
-		// Start the timer
-		$this->execTime = -microtime(true);
 		// Convert PHP errors to exceptions
 		set_error_handler([$this, 'exceptionErrorHandler'], E_ALL);
 	}
@@ -210,6 +215,11 @@ protected function showSummary(array $headers, ?array $rows, OutputInterface $ou
 			$rows[] = $this->filesCounter;
 			$rows[] = $niceDate;
 		}
+
+		$this->displayTable($output, $headers, $rows);
+	}
+
+	protected function displayTable($output, $headers, $rows): void {
 		$table = new Table($output);
 		$table
 			->setHeaders($headers)
@@ -250,9 +260,9 @@ protected function reconnectToDatabase(OutputInterface $output): Connection {
 	 * @throws NotFoundException
 	 */
 	private function getAppDataFolder(): Node {
-		$instanceId = $this->config->getSystemValue('instanceid', null);
+		$instanceId = $this->config->getSystemValueString('instanceid', '');
 
-		if ($instanceId === null) {
+		if ($instanceId === '') {
 			throw new NotFoundException();
 		}
 
diff --git a/apps/files/tests/Command/ScanAppDataTest.php b/apps/files/tests/Command/ScanAppDataTest.php
new file mode 100644
index 0000000000000..cdba710c2c8cf
--- /dev/null
+++ b/apps/files/tests/Command/ScanAppDataTest.php
@@ -0,0 +1,234 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH
+ * SPDX-FileContributor: Carl Schwan
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Files\Tests\Command;
+
+use OC\Files\Mount\ObjectHomeMountProvider;
+use OC\Files\Utils\Scanner;
+use OC\Preview\Db\Preview;
+use OC\Preview\Db\PreviewMapper;
+use OC\Preview\PreviewService;
+use OC\Preview\Storage\StorageFactory;
+use OCA\Files\Command\ScanAppData;
+use OCP\Files\Folder;
+use OCP\Files\IMimeTypeDetector;
+use OCP\Files\IMimeTypeLoader;
+use OCP\Files\IRootFolder;
+use OCP\Files\ISetupManager;
+use OCP\Files\NotFoundException;
+use OCP\Files\Storage\IStorageFactory;
+use OCP\IAppConfig;
+use OCP\IConfig;
+use OCP\IUser;
+use OCP\IUserManager;
+use OCP\IUserSession;
+use OCP\Server;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Group;
+use PHPUnit\Framework\MockObject\MockObject;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+use Test\TestCase;
+
+#[Group(name: 'DB')]
+class ScanAppDataTest extends TestCase {
+	private IRootFolder $rootFolder;
+	private IConfig $config;
+	private StorageFactory $storageFactory;
+	private OutputInterface&MockObject $output;
+	private InputInterface&MockObject $input;
+	private Scanner&MockObject $internalScanner;
+	private ScanAppData $scanner;
+	private string $user;
+
+	public function setUp(): void {
+		$this->config = Server::get(IConfig::class);
+		$this->rootFolder = Server::get(IRootFolder::class);
+		$this->storageFactory = Server::get(StorageFactory::class);
+		$this->user = static::getUniqueID('user');
+		$user = Server::get(IUserManager::class)->createUser($this->user, 'test');
+		Server::get(ISetupManager::class)->setupForUser($user);
+		Server::get(IUserSession::class)->setUser($user);
+		$this->output = $this->createMock(OutputInterface::class);
+		$this->input = $this->createMock(InputInterface::class);
+		$this->scanner = $this->getMockBuilder(ScanAppData::class)
+			->onlyMethods(['displayTable', 'initTools', 'getScanner'])
+			->setConstructorArgs([$this->rootFolder, $this->config, $this->storageFactory])
+			->getMock();
+		$this->internalScanner = $this->getMockBuilder(Scanner::class)
+			->onlyMethods(['scan'])
+			->disableOriginalConstructor()
+			->getMock();
+		$this->scanner->method('getScanner')->willReturn($this->internalScanner);
+
+		$this->scanner->method('initTools')
+			->willReturnCallback(function () {});
+		try {
+			$this->rootFolder->get($this->rootFolder->getAppDataDirectoryName() . '/preview')->delete();
+		} catch (NotFoundException) {
+		}
+
+		Server::get(PreviewService::class)->deleteAll();
+
+		try {
+			$appDataFolder = $this->rootFolder->get($this->rootFolder->getAppDataDirectoryName());
+		} catch (NotFoundException) {
+			$appDataFolder = $this->rootFolder->newFolder($this->rootFolder->getAppDataDirectoryName());
+		}
+
+		$appDataFolder->newFolder('preview');
+	}
+
+	public function tearDown(): void {
+		Server::get(IUserManager::class)->get($this->user)->delete();
+		Server::get(IUserSession::class)->setUser(null);
+		$this->rootFolder->get($this->rootFolder->getAppDataDirectoryName())->delete();
+		parent::tearDown();
+	}
+
+	public function testScanAppDataRoot(): void {
+		$homeProvider = Server::get(ObjectHomeMountProvider::class);
+		$user = $this->createMock(IUser::class);
+		$user->method('getUID')
+			->willReturn('foo');
+		if ($homeProvider->getHomeMountForUser($user, $this->createMock(IStorageFactory::class)) !== null) {
+			$this->markTestSkipped();
+		}
+
+		$this->input->method('getArgument')->with('folder')->willReturn('');
+		$this->internalScanner->method('scan')->willReturnCallback(function () {
+			$this->internalScanner->emit('\OC\Files\Utils\Scanner', 'scanFile', ['path42']);
+			$this->internalScanner->emit('\OC\Files\Utils\Scanner', 'scanFolder', ['path42']);
+			$this->internalScanner->emit('\OC\Files\Utils\Scanner', 'scanFolder', ['path42']);
+		});
+		$this->scanner->expects($this->once())->method('displayTable')
+			->willReturnCallback(function (OutputInterface $output, array $headers, array $rows): void {
+				$this->assertEquals($this->output, $output);
+				$this->assertEquals(['Previews', 'Folders', 'Files', 'Elapsed time'], $headers);
+				$this->assertEquals(0, $rows[0]);
+				$this->assertEquals(2, $rows[1]);
+				$this->assertEquals(1, $rows[2]);
+			});
+
+		$errorCode = $this->invokePrivate($this->scanner, 'execute', [$this->input, $this->output]);
+		$this->assertEquals(ScanAppData::SUCCESS, $errorCode);
+	}
+
+
+	public static function scanPreviewLocalData(): \Generator {
+		yield 'initial migration done' => [true, null];
+		yield 'initial migration not done' => [false, false];
+		yield 'initial migration not done with legacy paths' => [false, true];
+	}
+
+	#[DataProvider(methodName: 'scanPreviewLocalData')]
+	public function testScanAppDataPreviewOnlyLocalFile(bool $migrationDone, ?bool $legacy): void {
+		$homeProvider = Server::get(ObjectHomeMountProvider::class);
+		$user = $this->createMock(IUser::class);
+		$user->method('getUID')
+			->willReturn('foo');
+		if ($homeProvider->getHomeMountForUser($user, $this->createMock(IStorageFactory::class)) !== null) {
+			$this->markTestSkipped();
+		}
+		$this->input->method('getArgument')->with('folder')->willReturn('preview');
+
+		$file = $this->rootFolder->getUserFolder($this->user)->newFile('myfile.jpeg');
+
+		if ($migrationDone) {
+			Server::get(IAppConfig::class)->setValueBool('core', 'previewMovedDone', true);
+			$preview = new Preview();
+			$preview->generateId();
+			$preview->setFileId($file->getId());
+			$preview->setStorageId($file->getStorage()->getCache()->getNumericStorageId());
+			$preview->setEtag('abc');
+			$preview->setMtime(1);
+			$preview->setWidth(1024);
+			$preview->setHeight(1024);
+			$preview->setMimeType('image/jpeg');
+			$preview->setSize($this->storageFactory->writePreview($preview, 'preview content'));
+			Server::get(PreviewMapper::class)->insert($preview);
+
+			$preview = new Preview();
+			$preview->generateId();
+			$preview->setFileId($file->getId());
+			$preview->setStorageId($file->getStorage()->getCache()->getNumericStorageId());
+			$preview->setEtag('abc');
+			$preview->setMtime(1);
+			$preview->setWidth(2024);
+			$preview->setHeight(2024);
+			$preview->setMax(true);
+			$preview->setMimeType('image/jpeg');
+			$preview->setSize($this->storageFactory->writePreview($preview, 'preview content'));
+			Server::get(PreviewMapper::class)->insert($preview);
+
+			$preview = new Preview();
+			$preview->generateId();
+			$preview->setFileId($file->getId());
+			$preview->setStorageId($file->getStorage()->getCache()->getNumericStorageId());
+			$preview->setEtag('abc');
+			$preview->setMtime(1);
+			$preview->setWidth(2024);
+			$preview->setHeight(2024);
+			$preview->setMax(true);
+			$preview->setCropped(true);
+			$preview->setMimeType('image/jpeg');
+			$preview->setSize($this->storageFactory->writePreview($preview, 'preview content'));
+			Server::get(PreviewMapper::class)->insert($preview);
+
+			$previews = Server::get(PreviewService::class)->getAvailablePreviews([$file->getId()]);
+			$this->assertCount(3, $previews[$file->getId()]);
+		} else {
+			Server::get(IAppConfig::class)->setValueBool('core', 'previewMovedDone', false);
+			/** @var Folder $previewFolder */
+			$previewFolder = $this->rootFolder->get($this->rootFolder->getAppDataDirectoryName() . '/preview');
+			if (!$legacy) {
+				foreach (str_split(substr(md5((string)$file->getId()), 0, 7)) as $subPath) {
+					$previewFolder = $previewFolder->newFolder($subPath);
+				}
+			}
+			$previewFolder = $previewFolder->newFolder((string)$file->getId());
+			$previewFolder->newFile('1024-1024.jpg');
+			$previewFolder->newFile('2024-2024-max.jpg');
+			$previewFolder->newFile('2024-2024-max-crop.jpg');
+
+			$this->assertCount(3, $previewFolder->getDirectoryListing());
+
+			$previews = Server::get(PreviewService::class)->getAvailablePreviews([$file->getId()]);
+			$this->assertCount(0, $previews[$file->getId()]);
+		}
+
+		$mimetypeDetector = $this->createMock(IMimeTypeDetector::class);
+		$mimetypeDetector->method('detectPath')->willReturn('image/jpeg');
+
+		$appConfig = $this->createMock(IAppConfig::class);
+		$appConfig->method('getValueBool')->with('core', 'previewMovedDone')->willReturn($migrationDone);
+
+		$mimetypeLoader = $this->createMock(IMimeTypeLoader::class);
+		$mimetypeLoader->method('getMimetypeById')->willReturn('image/jpeg');
+
+		$this->scanner->expects($this->once())->method('displayTable')
+			->willReturnCallback(function ($output, array $headers, array $rows): void {
+				$this->assertEquals($output, $this->output);
+				$this->assertEquals(['Previews', 'Folders', 'Files', 'Elapsed time'], $headers);
+				$this->assertEquals(3, $rows[0]);
+				$this->assertEquals(0, $rows[1]);
+				$this->assertEquals(0, $rows[2]);
+			});
+		$errorCode = $this->invokePrivate($this->scanner, 'execute', [$this->input, $this->output]);
+		$this->assertEquals(ScanAppData::SUCCESS, $errorCode);
+
+		/** @var Folder $previewFolder */
+		$previewFolder = $this->rootFolder->get($this->rootFolder->getAppDataDirectoryName() . '/preview');
+		$children = $previewFolder->getDirectoryListing();
+		$this->assertCount(0, $children);
+
+		Server::get(PreviewService::class)->deleteAll();
+	}
+}
diff --git a/build/psalm-baseline.xml b/build/psalm-baseline.xml
index 04c44c1d9b9c9..1163db1d93015 100644
--- a/build/psalm-baseline.xml
+++ b/build/psalm-baseline.xml
@@ -1287,9 +1287,6 @@
     <InvalidArgument>
       <code><![CDATA[[$this, 'exceptionErrorHandler']]]></code>
     </InvalidArgument>
-    <NullArgument>
-      <code><![CDATA[null]]></code>
-    </NullArgument>
   </file>
   <file src="apps/files/lib/Controller/ApiController.php">
     <DeprecatedMethod>
diff --git a/lib/private/Files/Cache/Scanner.php b/lib/private/Files/Cache/Scanner.php
index eeed52afe0b3b..140f840ba1fb5 100644
--- a/lib/private/Files/Cache/Scanner.php
+++ b/lib/private/Files/Cache/Scanner.php
@@ -438,7 +438,7 @@ protected function scanChildren(string $path, $recursive, int $reuse, int $folde
 	 * @param bool|IScanner::SCAN_RECURSIVE_INCOMPLETE $recursive
 	 */
 	private function handleChildren(string $path, $recursive, int $reuse, int $folderId, bool $lock, int|float &$size, bool &$etagChanged): array {
-		// we put this in it's own function so it cleans up the memory before we start recursing
+		// we put this in its own function so it cleans up the memory before we start recursing
 		$existingChildren = $this->getExistingChildren($folderId);
 		$newChildren = iterator_to_array($this->storage->getDirectoryContent($path));
 
diff --git a/lib/private/Files/Utils/Scanner.php b/lib/private/Files/Utils/Scanner.php
index 4c98f5d0f470b..d93b8370d7a37 100644
--- a/lib/private/Files/Utils/Scanner.php
+++ b/lib/private/Files/Utils/Scanner.php
@@ -57,7 +57,7 @@ class Scanner extends PublicEmitter {
 	protected int $entriesToCommit = 0;
 
 	public function __construct(
-		private string $user,
+		private ?string $user,
 		protected ?IDBConnection $db,
 		private IEventDispatcher $dispatcher,
 		protected LoggerInterface $logger,
diff --git a/lib/private/Preview/Db/Preview.php b/lib/private/Preview/Db/Preview.php
index fe2509158e8b7..a55d920cc3404 100644
--- a/lib/private/Preview/Db/Preview.php
+++ b/lib/private/Preview/Db/Preview.php
@@ -100,20 +100,30 @@ public static function fromPath(string $path, IMimeTypeDetector $mimeTypeDetecto
 		$preview->setFileId((int)basename(dirname($path)));
 
 		$fileName = pathinfo($path, PATHINFO_FILENAME) . '.' . pathinfo($path, PATHINFO_EXTENSION);
-		$ok = preg_match('/(([A-Za-z0-9\+\/]+)-)?([0-9]+)-([0-9]+)(-(max))?(-(crop))?\.([a-z]{3,4})/', $fileName, $matches);
+		$ok = preg_match('/(([A-Za-z0-9\+\/]+)-)?([0-9]+)-([0-9]+)(-(crop))?(-(max))?\.([a-z]{3,4})$/', $fileName, $matches);
 
 		if ($ok !== 1) {
-			return false;
+			$ok = preg_match('/(([A-Za-z0-9\+\/]+)-)?([0-9]+)-([0-9]+)(-(max))?(-(crop))?\.([a-z]{3,4})$/', $fileName, $matches);
+			if ($ok !== 1) {
+				return false;
+			}
+			[
+				2 => $version,
+				3 => $width,
+				4 => $height,
+				6 => $max,
+				8 => $crop,
+			] = $matches;
+		} else {
+			[
+				2 => $version,
+				3 => $width,
+				4 => $height,
+				6 => $crop,
+				8 => $max,
+			] = $matches;
 		}
 
-		[
-			2 => $version,
-			3 => $width,
-			4 => $height,
-			6 => $max,
-			8 => $crop,
-		] = $matches;
-
 		$preview->setMimeType($mimeTypeDetector->detectPath($fileName));
 
 		$preview->setWidth((int)$width);
diff --git a/lib/private/Preview/PreviewMigrationService.php b/lib/private/Preview/PreviewMigrationService.php
index cacdb89dc31da..d3db56fc69cb1 100644
--- a/lib/private/Preview/PreviewMigrationService.php
+++ b/lib/private/Preview/PreviewMigrationService.php
@@ -66,11 +66,11 @@ public function migrateFileId(int $fileId, bool $flatPath): array {
 			$path = $fileId . '/' . $previewFile->getName();
 			/** @var SimpleFile $previewFile */
 			$preview = Preview::fromPath($path, $this->mimeTypeDetector);
-			$preview->generateId();
-			if (!$preview) {
+			if ($preview === false) {
 				$this->logger->error('Unable to import old preview at path.');
 				continue;
 			}
+			$preview->generateId();
 			$preview->setSize($previewFile->getSize());
 			$preview->setMtime($previewFile->getMtime());
 			$preview->setOldFileId($previewFile->getId());
@@ -93,17 +93,17 @@ public function migrateFileId(int $fileId, bool $flatPath): array {
 			->setMaxResults(1);
 
 		$result = $qb->executeQuery();
-		$result = $result->fetchAllAssociative();
+		$result = $result->fetchAssociative();
 
-		if (count($result) > 0) {
+		if ($result !== false) {
 			foreach ($previewFiles as $previewFile) {
 				/** @var Preview $preview */
 				$preview = $previewFile['preview'];
 				/** @var SimpleFile $file */
 				$file = $previewFile['file'];
-				$preview->setStorageId($result[0]['storage']);
-				$preview->setEtag($result[0]['etag']);
-				$preview->setSourceMimeType($this->mimeTypeLoader->getMimetypeById((int)$result[0]['mimetype']));
+				$preview->setStorageId($result['storage']);
+				$preview->setEtag($result['etag']);
+				$preview->setSourceMimeType($this->mimeTypeLoader->getMimetypeById((int)$result['mimetype']));
 				$preview->generateId();
 				try {
 					$preview = $this->previewMapper->insert($preview);
diff --git a/lib/private/Preview/Storage/LocalPreviewStorage.php b/lib/private/Preview/Storage/LocalPreviewStorage.php
index d0d3aa2b10dec..229c95dab47a7 100644
--- a/lib/private/Preview/Storage/LocalPreviewStorage.php
+++ b/lib/private/Preview/Storage/LocalPreviewStorage.php
@@ -18,21 +18,18 @@
 use OCP\DB\Exception;
 use OCP\Files\IMimeTypeDetector;
 use OCP\Files\IMimeTypeLoader;
+use OCP\Files\IRootFolder;
 use OCP\Files\NotFoundException;
 use OCP\Files\NotPermittedException;
 use OCP\IAppConfig;
 use OCP\IConfig;
 use OCP\IDBConnection;
-use OCP\Snowflake\ISnowflakeGenerator;
 use Override;
 use Psr\Log\LoggerInterface;
 use RecursiveDirectoryIterator;
 use RecursiveIteratorIterator;
 
 class LocalPreviewStorage implements IPreviewStorage {
-	private readonly string $rootFolder;
-	private readonly string $instanceId;
-
 	public function __construct(
 		private readonly IConfig $config,
 		private readonly PreviewMapper $previewMapper,
@@ -40,11 +37,9 @@ public function __construct(
 		private readonly IDBConnection $connection,
 		private readonly IMimeTypeDetector $mimeTypeDetector,
 		private readonly LoggerInterface $logger,
-		private readonly ISnowflakeGenerator $generator,
 		private readonly IMimeTypeLoader $mimeTypeLoader,
+		private readonly IRootFolder $rootFolder,
 	) {
-		$this->instanceId = $this->config->getSystemValueString('instanceid');
-		$this->rootFolder = $this->config->getSystemValue('datadirectory', OC::$SERVERROOT . '/data');
 	}
 
 	#[Override]
@@ -72,8 +67,12 @@ public function deletePreview(Preview $preview): void {
 		}
 	}
 
+	public function getRootFolder(): string {
+		return $this->config->getSystemValueString('datadirectory', OC::$SERVERROOT . '/data');
+	}
+
 	public function getPreviewRootFolder(): string {
-		return $this->rootFolder . '/appdata_' . $this->instanceId . '/preview/';
+		return $this->getRootFolder() . '/' . $this->rootFolder->getAppDataDirectoryName() . '/preview/';
 	}
 
 	private function constructPath(Preview $preview): string {
@@ -113,16 +112,19 @@ public function migratePreview(Preview $preview, SimpleFile $file): void {
 	public function scan(): int {
 		$checkForFileCache = !$this->appConfig->getValueBool('core', 'previewMovedDone');
 
+		if (!file_exists($this->getPreviewRootFolder())) {
+			return 0;
+		}
 		$scanner = new RecursiveDirectoryIterator($this->getPreviewRootFolder());
 		$previewsFound = 0;
+		$skipFiles = [];
 		foreach (new RecursiveIteratorIterator($scanner) as $file) {
-			if ($file->isFile()) {
+			if ($file->isFile() && !in_array((string)$file, $skipFiles, true)) {
 				$preview = Preview::fromPath((string)$file, $this->mimeTypeDetector);
 				if ($preview === false) {
 					$this->logger->error('Unable to parse preview information for ' . $file->getRealPath());
 					continue;
 				}
-				$preview->generateId();
 				try {
 					$preview->setSize($file->getSize());
 					$preview->setMtime($file->getMtime());
@@ -139,23 +141,34 @@ public function scan(): int {
 
 					if ($result === false) {
 						// original file is deleted
+						$this->logger->warning('Original file ' . $preview->getFileId() . ' was not found. Deleting preview at ' . $file->getRealPath());
 						@unlink($file->getRealPath());
 						continue;
 					}
 
 					if ($checkForFileCache) {
-						$relativePath = str_replace($this->rootFolder . '/', '', $file->getRealPath());
-						$rowAffected = $qb->delete('filecache')
+						$relativePath = str_replace($this->getRootFolder() . '/', '', $file->getRealPath());
+						$qb = $this->connection->getQueryBuilder();
+						$result2 = $qb->select('fileid', 'storage', 'etag', 'mimetype', 'parent')
+							->from('filecache')
 							->where($qb->expr()->eq('path_hash', $qb->createNamedParameter(md5($relativePath))))
-							->executeStatement();
-						if ($rowAffected > 0) {
-							$this->deleteParentsFromFileCache(dirname($relativePath));
+							->runAcrossAllShards()
+							->setMaxResults(1)
+							->executeQuery()
+							->fetchAssociative();
+
+						if ($result2 !== false) {
+							$qb->delete('filecache')
+								->where($qb->expr()->eq('fileid', $qb->createNamedParameter($result2['fileid'])))
+								->andWhere($qb->expr()->eq('storage', $qb->createNamedParameter($result2['storage'])))
+								->executeStatement();
+							$this->deleteParentsFromFileCache((int)$result2['parent'], (int)$result2['storage']);
 						}
 					}
 
-					$preview->setStorageId($result['storage']);
+					$preview->setStorageId((int)$result['storage']);
 					$preview->setEtag($result['etag']);
-					$preview->setSourceMimetype($this->mimeTypeLoader->getMimetypeById($result['mimetype']));
+					$preview->setSourceMimetype($this->mimeTypeLoader->getMimetypeById((int)$result['mimetype']));
 					$preview->generateId();
 					// try to insert, if that fails the preview is already in the DB
 					$this->previewMapper->insert($preview);
@@ -169,6 +182,8 @@ public function scan(): int {
 						if (!$ok) {
 							throw new LogicException('Failed to move ' . $file->getRealPath() . ' to ' . $previewPath);
 						}
+
+						$skipFiles[] = $previewPath;
 					}
 				} catch (Exception $e) {
 					if ($e->getReason() !== Exception::REASON_UNIQUE_CONSTRAINT_VIOLATION) {
@@ -182,65 +197,45 @@ public function scan(): int {
 		return $previewsFound;
 	}
 
-	private function deleteParentsFromFileCache(string $dirname): void {
+	/**
+	 * Recursive method that deletes the folder and its parent folders if it's not
+	 * empty.
+	 */
+	private function deleteParentsFromFileCache(int $folderId, int $storageId): void {
 		$qb = $this->connection->getQueryBuilder();
-
 		$result = $qb->select('fileid', 'path', 'storage', 'parent')
 			->from('filecache')
-			->where($qb->expr()->eq('path_hash', $qb->createNamedParameter(md5($dirname))))
+			->where($qb->expr()->eq('parent', $qb->createNamedParameter($folderId)))
 			->setMaxResults(1)
 			->runAcrossAllShards()
 			->executeQuery()
-			->fetchAll();
+			->fetchAssociative();
 
-		if (empty($result)) {
+		if ($result !== false) {
+			// there are other files in the directory, don't delete yet
 			return;
 		}
 
-		$this->connection->beginTransaction();
-
-		$parentId = $result[0]['parent'];
-		$fileId = $result[0]['fileid'];
-		$storage = $result[0]['storage'];
-
-		try {
-			while (true) {
-				$qb = $this->connection->getQueryBuilder();
-				$childs = $qb->select('fileid', 'path', 'storage')
-					->from('filecache')
-					->where($qb->expr()->eq('parent', $qb->createNamedParameter($fileId)))
-					->hintShardKey('storage', $storage)
-					->executeQuery()
-					->fetchAll();
+		// Get new parent
+		$qb = $this->connection->getQueryBuilder();
+		$result = $qb->select('fileid', 'path', 'parent')
+			->from('filecache')
+			->where($qb->expr()->eq('fileid', $qb->createNamedParameter($folderId)))
+			->andWhere($qb->expr()->eq('storage', $qb->createNamedParameter($storageId)))
+			->setMaxResults(1)
+			->executeQuery()
+			->fetchAssociative();
 
-				if (!empty($childs)) {
-					break;
-				}
+		if ($result !== false) {
+			$parentFolderId = (int)$result['parent'];
 
-				$qb = $this->connection->getQueryBuilder();
-				$qb->delete('filecache')
-					->where($qb->expr()->eq('fileid', $qb->createNamedParameter($fileId)))
-					->hintShardKey('storage', $result[0]['storage'])
-					->executeStatement();
-
-				$qb = $this->connection->getQueryBuilder();
-				$result = $qb->select('fileid', 'path', 'storage', 'parent')
-					->from('filecache')
-					->where($qb->expr()->eq('fileid', $qb->createNamedParameter($parentId)))
-					->setMaxResults(1)
-					->hintShardKey('storage', $storage)
-					->executeQuery()
-					->fetchAll();
-
-				if (empty($result)) {
-					break;
-				}
+			$qb = $this->connection->getQueryBuilder();
+			$qb->delete('filecache')
+				->where($qb->expr()->eq('fileid', $qb->createNamedParameter($folderId)))
+				->andWhere($qb->expr()->eq('storage', $qb->createNamedParameter($storageId)))
+				->executeStatement();
 
-				$fileId = $parentId;
-				$parentId = $result[0]['parent'];
-			}
-		} finally {
-			$this->connection->commit();
+			$this->deleteParentsFromFileCache($parentFolderId, $storageId);
 		}
 	}
 }