Iron Citadel can't be completed (even with rares monsters + boss, all killed)

Same to me.
Boss killed, looted the artefacts, 0 mob left, but even if still in the map and press "U" I can see the map "failed".
I have run 3 of them and all in the same state: Failed.

Annoying but not so much, I can have access to adjacent locations and got the loot.