You can skip him.
Just run past him, let one person die, CR that person, wipe. After wipe CR person rezzes rest of the group. Proceed.
Another way is to kite him waaaaaaaay from his location and just fight him there. His immunity buff is timed, thus if u kite him enough you wont have to fight adds (or too many of them).
Ofc, bug should be fixed, but you can still do it.