I ran 6 chars through that boss and it reset at least once on all six attempts. It reset TWICE on 4 attempts. In every case, we had at least one member alive and attacking the WB when it reset. It appears (to untrained eyes) to reset after it pulls everyone in and stuns them for a sec. We did have companions standing off and shooting ranged weaps. Still, seeing a WB reset so many times seems off.
I thought maybe someone ran off but every group member was in-range and attacking the boss when the reset occurred. I'm not entirely sure this is a bug or something we were doing wrong. Can anyone else confirm or weigh in, pls?