Bug report. Sometimes the thief clime ability disappears. The only fix is to reload a save. If you save after it disappears then it's permanent for that save. It seems to happen the most when you first clime at the three seals
One of the areas you need a canon to blast through. Seems the door got fixed for some reason. I tried climbing the way back but once I reach the top nothing happens. Wanted to kill some skeletons to unlock there CG's