There are two Catch-22 contradictions in the adventure.
The first is in Crypt of the Talhund. The haunting in area 16 can only be put to rest by defeating the mummy in area 17, whereas the mummy in area 17 can be prevented from animating if all the haunts have been put to rest. Except that latter trigger is impossible unless the mummy has already been defeated to end the haunt, in which case it can't animate anyway.
The other is in the Briny Maze. The rods in B7 open the doors between B13 & B14, but the beholder in B14 immediately closes the doors again. The party can't get through those doors to remove the beholder without activating the rods, but he'll close the door before they get to him every time they do. The only way around this is if they somehow figure out that the doors are being opened but then immediately closed again by someone on the other side, have most of the party wait just outside the doors while one goes all the way back to activate the rods and open the doors, then take out the beholder (or at least distract it) while waiting for that hapless volunteer to return.