Only the Devs will know why this was even touched in the update, but whatever. Someone messed with the clear texture of the "wall" separating rooms in dungeons and now many doorways are just black holes. They can be passed, but one cannot see through. When you stand next to the black texture and move the mouse up to look downwards, the 1 pixel thick texture "wall" becomes visible. Sometimes it occurs in doorways, sometimes the wall is some dozen pixels behind a door.

Every player in the group sees the same black walls, so it's not a client side issue.

I'm not going to list all dungeons, but Dread Cellar maybe a start.