Yeah it has become so common now that if any group wipes in ct I fear for a glitch sadly. I have heard rumors about it being caused by a player DCing in the middle of the match and dying/Pets so on and so forth. I wish I had an exact answer of why or how it keeps happening. Only bosses I haven't had it occur on is King Behemoth and the last banana guy boss everywhere else it could be my worst nightmare.