I put Caracalla's soul to rest by keeping the candles lit and killing all the Invisible Terrors. I completed the quest, got my rewards and the portal got activated. I took the portal to the locked room, looted the chest except for the gold chest at the SW corner. While trying to figure out how to open it, I wanted to see if there were any buttons behind it. So, when I jumped behind the chest, I found myself on the other side of the wall. I have duplicated this several times. You can walk through both the S wall or the W wall right behind the chest. You cannot walk back though. There's another building back there with the same walls, windows and the flooring, no furniture. There's a black void where it seems a door would go and if you step through it, you find yourself falling in pitch black with zero visibility. If you run in any direction, the "Auto Unstuck" feature of the game puts you back in the room with the gold chest.
Has any body experienced this?