Stone Citadel not completing

I killed all but one mob which I couldn't find after covering the whole map.
Boss was dead and fragments harvested. But the citadel was still 'In Progress' and once I'd left and moved on it quickly changed to Failed, blocking a path on atlas map. Surely this is an easy fix. Both Stone and Iron citadels not 'completing'? This has been issue for a long time.

I have the same issue with any Stone Citadel map or Iron Citadel.. entire map is cleared 0 monsters remain and the map won't complete. Sometimes blocking my path :(

This has been known for months. Neither Iron nor Stone citadels can be completed, because the boss kill doesn't count for some reason.

Check the monster counter, it will remain at 1 even if you've killed everything.