Final objective for the Wretched Delve dungeon requires me to destroy three Fallen Idols. Only two spawned. There is an area where it is likely that the third one was supposed to spawn, but in its place was an event.
UPDATE: I reset the dungeon. The event now spawned in an earlier part of the dungeon, freeing up room for the Fallen Idol objective to function properly.
Solution: Remove Dungeon Events. I do not believe anyone does those anyway.