Invincible mobs on chaos trial

Been farming chaos trials all day, and ran into invincible mobs.
Nothing can damage them. Health bars dont even pop up. And no I wasn't picking + mob resist as a modifier or whatever - I was killed by mobs who wouldn't take any damage. I was blinking around trying to escape so my mnions could thin them out...all of a sudden nothing takes any damage at all.

Nothing.

No damage.

GGG can check the logs.