Thanks for trying it out anyway!
GMS has some weird issues with performance, sometimes just running the game again shoots it back up to 60fps, but I'm studying ways to make it more optimized. There's no mouse acceleration at all for the camera, but the vertical part of it is like modded z-axis for DOOM, so it can feel weird. Locked doors are never in the way to the exit, that floor probably had a secret wall you could open to advance. You can find those by paying attention to out of place walls, or the [E] prompt when looking at them. And finally, that isn't a bug, you just got blinded by a spell.