Problem is that skills like the one from NotB Eddie apply the debuff "after" the attack. So if you kill the dog, the perfect death is not applied. I never killed both doggos at once, but it still worked. First strip off the immunity without doing too much damage. Then apply perfect death and then kill the first dog. This way it worked most of the times. Sometimes something went wrong and the loop started. Then you need to exit the battle and try again. Stupid! Maybe they fix it soon, but who knows?