I think it happened when I was just opening a door. It didn't go through with opening it and froze at that point. It was level 2 or 3 when it occurred. Didn't notice anything else unusual but I'll be sure to report more details if it happens again.
In any case, amazing work with the game! Even though it's simple, it's super fun. Also loving your pixel art in your other works.
EDIT: Had this happen a few times - when going to the next level, I spawned on top or next to a monster which made taking a hit unavoidable. Perhaps consider a safe area of minimum 1-2 squares around the character or making him always spawn in a small empty room.
EDIT 2: The freezing bug happened again, and yes it was when going to the next level.
EDIT 3: Sometimes it's not possible to find the exit. Given that it can also occur that some objects spawn on top of each other, it's possible that a chest occupies the same space as the exit, blocking it.