Playing solo, fully cleared the Sealed Archives up to the Archive Door which I can’t open. I still have “Slay the Decayed Keymaster and collect the Rotten Key” as an objective.
I’ve gone through the dungeon completely, explored every nook and cranny, killed every monster, smashed every breakable, opened every chest, picked up every item. No key, can’t open the door. Can’t complete the dungeon.