Bugged parasitic eximi in sortie

[(PSN)Lord_Gremlin]

Today I've done sortie solo as ash prime. During final mission, infested survival ALL parasitic eximi were unkillable by bladestorm. Since I was solo I was able to test it thoroughly, on single parasitic eximus multiple times, to make sure it's not an aura effect or anything. They take damage, for example 5970 from bladestorm and then their healthbar instantly becomes full again. Definitely a bug here. Weapons killed them normally. Is it PS4 only? Did I see a unique bug or somebody can reproduce it? Can't test again obviously, unless someone would taxi me there again.