Not sure if hiding spoilers matters in bug reports but just to be safe:
The bug is just after the room
After doing this, the player opens a crawlspace and climbs into it.
Once the player is in the crawlspace, the door to it closes. The game then pauses for a second, presumably loading the next part of the map.
Prior to the game loading the next part, however, the small door to the crawlspace isn't solid and the player can clip through it, leading out of the tunnel and back into the room, which has already unloaded and is now a void. By the time the player does this, the game will usually load the next part of the map, causing the door to become solid and trapping them in the void area, where they can easily fall off the map entirely.