I just had a dungeon rolled with no route to the exit.
I left and came back, and the next time there was no passage out of the starting room.
These random mishaps are made more serious by the fact that this game is very good at preventing savescumming. I have no recourse but to retreat from the dungeon with nothing, wasting a day.
(In case it matters, this is an elite cavern mission provided as part of a quest.)