There appears to be a bug where you can step off the stairs while going up them before you fully step through them and the next room will load (or be half visible) but the collision appears to be of the room under it.
I took a video of it, how to reproduce it here.
youtu.be/Qwi1K7-7otw
[video]
https://youtu.be/Qwi1K7-7otw[/video]