Untargetable and immortal rare in boss arena in Vaal Foundry

https://i.postimg.cc/1XjtXMbc/BF7980-E2-09-A9-4-EED-8831-836-F2-DB01828.png

The rare can't be targeted.
3 rares spawned in this arena, one of them was an essence.
I have Deadly Evolution and Twin Threats in atlas skill tree, but I don't think it was applied here (these were 3 different rares, not duped).

The rare can damage and kill me.

Leaving and coming back doesn't fix it.
Doing the ritual visible in the screenshot doesn't fix it.

I don't remember the name of the enemy that the rare is, but it's the small automaton that shoots bolts at you from both arms.