Boss on cleansed map makes ritual unfinishable

firstly, sorry for my English because it's not my first language
So I got this bug twice and I can confirm that both times have one thing in common is The boss that spawn on cleansed map (The Immured fury, I don't remember if it's correct) when this boss died in ritual's area and activate ritual afterward seem like ritual tries so spawn the boss, but it can't actually spawn but the ritual count that it spawned that boss and it still in ritual and have to be killed for ritual to be ended but didn't spawn any.

I can confirm that it tried to spawn a boss back because whenever I use warcry skill with raging cry it'll generate me 16 rage