I just encountered this bug when trying to complete the dungeon, it occasionally won’t let me attack the door anymore and asks me to “Slay the Ghouls” even after killing all of them. I’ve reset multiple times and get the same result.
Here’s a forum link from June 2023 explaining the issue: By Three They Come bugged, cannot progress - #17 by Cujoman187-1166
The issue seems to occur if you kill enemies too quickly after they become targetable (so minion classes and classes that can preload damage like my blizzard sorcerer suffer the most).
This bug also occurs in other sidequests that require you to kill enemies. In one sidequest (I forget the name of) I had to protect a girl from villagers, I preloaded damage on them when they appeared and they instantly died when they became targetable. This broke the quest and would not allow me to progress, meaning I had to reset the dungeon before continuing.
The only “temporary” fix is to do nothing for a while until all enemies have spawned in or are targetable, then kill them all at once.
I just don’t understand how this bug still exists a year later after it has already been reported.