Not sure if this is a known issue as its been here ever since the introduction of the rogue class.
If a decoy totem with the fear node spec’d on mobs in the arena sometimes causes them to be feared into walls then get collision stuck. Its quite noticeable because every 5 waves you stand around realizing there are no monsters left and have to run around the edge of the arena looking for the one mob stuck against a wall you have to clear before you can get the dialog to start the next 5 waves.