Well, we have seen Burblespue Halescourge do his comatose thing a few times already.
Today, for the 1st time, I saw Bödvarr Ribspreader turning slowly and continuously in the middle of his arena, as if acknowledging an imagined crowd. No additional minions entered the arena, and he did not do anything other than turn slowly. All I had to do was to land headshots until he ran out of HP.
There are 4 noteworthy console logs for that day. I cannot remember what time of day it was, but the bug probably occurred during one of the shorter morning sessions.