This seems to be a stupid bug that I encountered with some other games as well. Kiana, that is the reason why I made my post here some months ago. The problem still exists, the itch app says "not available".
That is really strange! I wonder if it's been fixed in the latest version of GMS2. We converted the project for the original alpha build recently and it broke some stuff, but we fixed everything and re-exported it with some game feel improvements.