Same issue here as well. I ended up changing world tier down and back up again to reset the dungeon (not sure if there is a faster way to do this). When I loaded back into the reset dungeon the layout was different.
The first layout as soon as I came in I was forced to take a left (NW). The barrier to the next stage was at the end of this single hallway (NW corner of available map). But there were also branches going off of this long hallway going to the NE and SE. When I reset the dungeon I had the option to go left (NW) or right (SE) at the entrance. It appears that the original layout has an issue where it can spawn a prisoner somewhere past the barrier, would be my guess. Thankfully I wasn’t doing a Nightmare dungeon.