Had this situation a couple of times now. The forest keeper mobs in jungle become immune to most of my damage. I fought them multiple times, multiple of keepers at the same time too. Some of them take steady damage and die no problem, but there are few time afte time that are "immune". I have loads of physical, poison and a bit of magic damage on paladin (some bits of rainbow dmg from charms). The pic below - atacking mobs for over a minute with same results - switched to tantrum with fire bombs quiver proc - same, no damage. I was guessing that keeper casts some sort of idol of sosglen clone skill that temporary makes him super tanky. But that is not it, others keepers die np after their nova atack. Also mob is not healing when atacking me or when chasing me, runing back from mob and atacking again does not reset his immunity in most cases i tried.