GPA was/is glitched?

Your class needs to be one that has a summon. It's very hard to avoid killing the extra B if you do not have a summon.

None of the extra mobs pass the invisible barrier so if you keep the battle to the far right its pretty much impossible to DC.. The only class i can think of that would have any form of issue is perhaps shadower, ME always KBs to the left so you would have to be careful and make sure the boss doesn't stray too far left.