After zoning into the chaos cave at CRP the first mob could be killed without probs with a Doombeamer.
The second mob was down to 10% health when it looked like it wasn't losing health anymore.
Switching to another weapon (Cursed Soul) made it possible to kill the mob.
However, the next mob can't be damaged by either weapon. The mob does not attack and does not move around.
Moving further to the next cluster of mobs changed the behavior again. Suddenly they were able to attack again.