Unkillable Rare enemy, hitbox below floor collision box

The enemy was on a high level of the map and I guess spawned below the floor collider plane. It doesn't seem to take damage from me, corpse explosions via herald of ice, or ground effects like Salvo. It blocked the map completion so also it wasn't "dead" and continuing to fight. While I can't hit it, it can still attack and kill me freely.

I had a similar issue with unkillable rare monster (and a host of its minions). See my thread for details: https://www.pathofexile.com/forum/view-thread/3654841

Idk if you have an essence encounter in your map. Let us know and if you can solve it same way.

Hey, its explicit this mob, as it seems.
I have the same issue with this mob in Vaal Factory now.