The Feared - Sirus not witnessed after defeat

Hi.

I've defeated Sirus 3 times now and 3 times has he not been witnessed by the Maven after the fight concluded. (Yes, Maven was present during those fights)
I suspect my progression might be bugged, because before those 3 tries, I had a bugged encounter with that Boss. On my first attempt, the fight ended unexpectedly in the first round of the fight, as he came down from his throne, ate a Obliteration Chaos Explosion from Veritania and jumped back onto his throne. The game however gave me then a notification that I unlocked a favourite map slot, all the Sirus bubbles faded out and Sirus himself was just sitting in the Air doing nothing (Maven however was still mad, probably because of the short fight). Got no loot drops either.

As things stand, I cannot currently do The Feared at all.
plz help

Here is a screenshot of the end of that bugged first fight.