Ritual cannot be completed - Cleansed unique Boss

I had ritual - last one(4/4) - in map Hidden Grotto (around 18:30 CET). Unique boss from Cleansed spawned in ritual area before I started ritual, i killed him, then I started ritual and when I killed all mobs ritual cant finish (ran around for like 2 mins trying to find some missing mobs but no luck). It looks like that Cleansed boss somehow bugged it, it never happened to me before - also never had that CLeansed boss spawned in ritual area before. I had to port out to HO and go next map.

Check it GGG ;)