map completion (citadel)

I completed the boss and looted a fragment in an Iron Citadel, but the map still said "in progress." I then searched every centimeter of the dungeon for the "1 monster left." There was one skull left in the whole instance, it was in the dead bosses room. I logged out figuring it was just bugged and would sort itself out, but I logged in a day later and it says "map failed." I guess it was bugged.