[Bug] Find and defeat the Royal Architect.

I kill them when he and me died, but cutscene are start, after some time I clicked reviev, killed again the boss and don't get completion of quest.
I continued playing the game, hoping that the bug would disappear after completing all the quests, but it didn't.
In endgame I returned to location of Royal Architect and killed him.
After this somehow cutsene replays again, and after watch it all, I don't get completion of quest again.
I don't know how to solve that bug. Please help!