EXC_BAD_ACCESS in MapboxCoreMaps when loading published Outdoors gallery template

[alpermat]

EXC_BAD_ACCESS in MapboxCoreMaps when loading published Outdoors gallery template

Environment

• Xcode version: 26.4
• iOS version: 26.4 (iPhone 17 Pro Simulator)
• macOS: 26.4.1
• Maps SDK Version: 11.21.1 (also reproduced on 11.21.0)

Observed behavior and steps to reproduce

Loading a freshly-published, unmodified copy of Mapbox's own Outdoors gallery template (https://www.mapbox.com/gallery → "Outdoors") in a minimal SwiftUI app crashes the app immediately on first render, inside MapboxCoreMaps during MetalView.draw.

The same style URI renders correctly in Mapbox Studio's web preview (GL JS), confirming the published style is valid. MapStyle.standard (without a custom URI) renders fine in the same minimal app — so the SDK, token, and project setup are all working. The crash is specific to loading a Standard-based custom style published from the Outdoors gallery template.

Minimal reproduction (~10 lines)

import SwiftUI
import MapboxMaps

@main
struct MapboxStyleTestApp: App {
    var body: some Scene {
        WindowGroup { ContentView() }
    }
}

struct ContentView: View {
    private let styleURI = StyleURI(rawValue: "mapbox://styles/<your-username>/<your-published-outdoors-id>")!

    var body: some View {
        Map()
            .mapStyle(MapStyle(uri: styleURI))
            .ignoresSafeArea()
    }
}

Steps:

1. In Mapbox Studio, open the Outdoors gallery template, click "Add to your Studio".
2. Without any edits, click Publish.
3. Copy the production Style URL.
4. Paste it into the snippet above.
5. Run on iOS 26.4 simulator (iPhone 17 Pro). App crashes on launch.

Expected behavior

The Outdoors gallery template — published by Mapbox itself — should render in the iOS SDK the same way it renders in Studio's web preview.

Crash log (excerpt)

Exception Type:    EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x0000000000000188

Thread 0 Crashed:: com.apple.main-thread
0   MapboxCoreMaps   0x10965cf6c  (+ 6721388)
1   MapboxCoreMaps   0x10967404c  (+ 6815820)
2   MapboxCoreMaps   0x109609594  (+ 6378900)
3   MapboxCoreMaps   0x10961d5ac  (+ 6460844)
4   MapboxCoreMaps   0x10918e158  (+ 1679704)
5   MapboxCoreMaps   0x1091863c8  (+ 1647560)
6   MapboxStyleTest  thunk for @escaping @callee_unowned @convention(block) () -> ()
7   MapboxStyleTest  MetalView.draw(_:)  (MetalView.swift:75)
8   MapboxStyleTest  @objc MetalView.draw(_:)
9   MetalKit         -[MTKView draw] + 132
10  MapboxStyleTest  MapView.updateFromDisplayLink(displayLink:)  (MapView.swift:731)
11  MapboxStyleTest  closure #1 in MapView.didMoveToWindow()  (MapView.swift:773)

A [Warning, mapbox-styles] is also logged before the crash:

The expression config "theme" is missing in style

Notes / preliminary analysis

• Reproduces on a clean SwiftUI project with no custom code paths beyond the snippet above.
• Reproduces with the freshly-published gallery template (no Studio edits) and with a customized derivative.
• Does not reproduce when using MapStyle.standard or MapStyle.standard(lightPreset: .night) — only when loading a Standard-based custom style URI.
• The expression config "theme" is missing warning suggests the style references a ["config", "theme"] expression that isn't resolved at the outer style level, possibly related.

Additional links and references

Style URI used in repro: mapbox://styles/alpermat/cmo0520w800a501sddzpzcg1k (a freshly-published, unmodified Outdoors gallery template — happy to share the specific URI privately if it helps).

Crash log and the test repo are attached.

MapboxStyleTest-2026-04-15-172627.ips.zip

MapboxStyleTest.zip

[alpermat]

Root cause: root-level terrain field in the published style

Filed the issue myself — following up with the actual root cause after debugging further.

I fetched the published style JSON via the Styles API and found that when Mapbox Studio publishes the Outdoors gallery template, it emits a top-level terrain field on the root style (not just via the Standard import):

"terrain": {
  "source": "mapbox-dem",
  "exaggeration": [
    "interpolate", ["linear"], ["zoom"],
    6, 0,
    7, 1.2
  ]
}

Terrain exaggeration ramps from 0 → 1.2 between zoom 6 and 7. The crash reliably triggers when the camera crosses that zoom threshold — i.e. terrain rendering actually activates. That matches my original repro ("zoom in twice from a world view, crash").

Other smells in the same published JSON

• Duplicate DEM sources: mapbox://mapbox.mapbox-terrain-dem-v1 and mapbox-dem are both declared with identical URLs. Redundant but probably not crash-relevant.
• Fog references ["config", "theme"] at the root level, but theme is a config property of the basemap import, not the root — this is the source of the [Warning, mapbox-styles] The expression config "theme" is missing in style warning from the original report. Doesn't crash on its own.

Workaround

Calling style.removeTerrain() on style-load works around the crash:

Map(viewport: $viewport)
    .mapStyle(MapStyle(uri: <outdoors-template-uri>))
    .onStyleLoaded { _ in
        proxy.map?.removeTerrain()
    }

After the fix, zooming past the 6→7 threshold is stable and hillshade/contours/labels still render correctly. The template remains usable — just without the 3D terrain it ships with.

Confirmed affected versions

• MapboxMaps 11.21.0, 11.21.1, 11.22.0-rc.1, 11.22.0 (all crash)
• iPhone 17 Pro simulator, iOS 26.4, Xcode 26
• Fresh app container (not a cache issue)

Happy to share the full style JSON privately if it's useful to Mapbox's style team.

[parrots]

I'm seeing this happen on-device, too, with 11.21.0 and 11.22.0. This is our top crasher in crashlytics atm.

Steps to reproduce:
1 - Load a style that doesn't use terrain
2 - Ensure you're zoomed in far enough to trigger terrain in the next style
3 - Swap to a style that loads terrain

The terrain-enabled style loads OK if I start zoomed out far enough. But if I try to load it while at zoom level 10+, it'll crash.

My symbolicated crash from production:

Crashed: com.apple.main-thread
0  MapboxCoreMaps                 0x67927c mapbox::maps::Version::getRevisionString() + 4468408
1  MapboxCoreMaps                 0x6905b0 mapbox::maps::Version::getRevisionString() + 4563436
2  MapboxCoreMaps                 0x625618 mapbox::maps::Version::getRevisionString() + 4125268
3  MapboxCoreMaps                 0x639a10 mapbox::maps::Version::getRevisionString() + 4208204
4  MapboxCoreMaps                 0x1a4f58 mapbox::maps::CoordinateBounds::extend(mapbox::maps::CoordinateBounds const&) const + 18672
5  MapboxCoreMaps                 0x19cf84 mapbox::maps::StyleManager::isStyleLoadingFinished() + 573564
6  Slopes                         0x100a15c @objc MetalView.draw(_:) + 75 (MetalView.swift:75)
7  MetalKit                       0x1fe4 -[MTKView draw] + 132

I can't seem to reproduce the issue with 11.20.3 FWIW.