The respawn in the Citadel and maybe the yard has changed. I did not time it but it felt like 2 min? Makes the boss events crazy if the trash is going to repawn in the room that fast.
I cleared the trash around Llivnu and the started placing my toons for a new strat I wanted to try. Got respawn while I was moving toons. Killed them again, then engaged Llivnu. Got the first adds killed and then respawn of the trash again.
Hopefully a bug =)