That sounds like a game bug, as the sandbox is doing what it should be doing, ie.:
- Granting permissions to itch-player before launch
- Launching as itch-player
- Denying permissions afterwards
I have a theory though: if the launcher exits, itch considers the game to have quit and will start denying permissions - that would explain why the game fails to load halfway through. If the launcher (resolution picker) would exec instead of fork, that would probably fix it! I'm not sure what your engine code looks like :)
Alternatively, it could fork, but then close the window and wait for the game to be finished before it exit()s.