Killed Copper Citadel Boss but nothing happened after - no quest completion

I killed the copper citadel boss but nothing happend to say I had completed a quest. There was no way to leave his chamber without a TP, he didn't drop a quest fragment.

Now the "Copper Citadel" node on my atlas says "failed" and I can't re-attempt it?

The exact same thing happend to me...no idea what to do