This never happened to me before, but since two or three weeks ago, whenever I participate in a dungeon or Saalus run with a character, at some point the client “freezes” (it stays responsive, as you can clearly move your character around, but cannot interact with your environment – this is really annoying, as you do not immediately detect the problem and could waste your run), often after 80-90% of map completion. The only way for me to fix the situation is to kill the ToS process in the taskbar and relaunch the game.
Note: this happens ALMOST EVERY TIME.
On a side note, the same problem happens randomly when switching maps. The little character that digs on the loading screen sometimes stops digging at roughly 70% and the client stays frozen. Then killing the process and restarting the client is the only way to fix that.