Vaal Foundry: Rare half stuck in floor, not targetable

In the Vaal Foundry map I have encountered a rare mob sunk half into the floor that cannot be targeted and effectively stops map completion. I have run the map 2 times in a row and encountered the same rare both times.

While the rare can't be targeted or affected by skills, it has no such issue and
happily enjoys it's invulnerable status while attacking constantly.

Don't know the rares name (as cannot target) but it has multiple arms and is holding two bows.