Fix commented-out Debug.Assert()s that are failing

[paulmedynski]

After enabling PR pipelines to run tests in Debug mode, several Debug.Assert()s were found to be failing. They have been commented out with a comment like this:

TODO(GH-3604): Fix this failing assertion.

Someone familiar with the intention of each assertion needs to figure out why they're failing and fix them.

[Wraith2]

Someone familiar with the intention of each assertion needs to figure out why they're failing and fix them.

Good luck finding them :(