Cannot get credit for defeating The Black Star

Title says it all. I've killed her four times using the quest item provided when I clear a t11+ map. The screenshot below shows the quest saying "Defeat the Black Star" when I'm clearly in an instance where she is defeated.

I defeated her alone. I use Herald of Agony/Arakaali's fang/Culling strike. I tried without Culling Strike, same result.

Help? Can't progress my storyline.



UPDATE: I went for the Eater of Worlds instead, got his miniboss and that managed to progress. I then re-acquired an invite for the Black Star, re-killed her and it progressed at that point. So somehow unstuck myself. So the immediate problem is solved, but there definitely was a bug there.