thanks for the replies so far

@jumpman we're currently trying to narrow it down. The problem is that the project is somewhat complex and simply commenting out parts of it doesn't really work without making bigger changes to it.
For now I'll focus on trying to make sure that no unwanted functions survive the level_load(). It might be AI or other gameplay related functions that are still running after unloading the level and keep using "freed" memory until it's assigned to something else (which makes it crash).

We're not 100% that this is the case, though.