Hand of chayula makes colossus invulnerable

Act 2 cruel playing with my SO.
She's playing a pathfinder that uses a level 12 hand of chayula with sockets: enfeeble, vulnerability and snipers mark.

Every time she cast that on zalmarath the colossus, we couldn't target him nor deal damage. Neither our minions nor AOE attacks could hit him. Simply needed to reset and not use hand of chonk to proceed passed this boss.