Yugul boss in Terrace map containing Drox's Citadel bugged between phases

bug report - 773 032 936

After going into one of their phases with the minions popping out, either one of the minions or yugul just stood around, couldn't be damaged, and did not do anything. I eventually died from all the balls hitting me.

This issue is only specific to certain map bosses which, if frozen, is unable to progress to the next phase.
Known issue.
Workaround: Leave the map, wait a few seconds for the boss to unfreeze, rejoin.