On the 3rd part of the Madness in the Mountains campaign, I had a Grintmaw Shaman equipped with a Magma Cloak. He was hit by an Arroyo Flamewisp and lost Fire Immunity and Frost Immunity. Subsequent Flamewisp attacks were damaging the Shaman.
I figured out that he was actually hit by a Riftlord, and there's an ability that says it removes an ability when the attack is successful. While Immunity Fire is an ability, I wouldn't expect abilities granted by equipment would be removed. In another play of the same stage, I had another Molten Cloak on a Draksar Spellsword, and the Trail Lava was removed.
Hmmm. I suspect this is unique to that one rift lords in- campaign ability. Could be wai, though I think it would be more thematic/immersive were it not (and that *is* the campaigns primary goal right? A thematic and immersive story?). @Sokolov thoughts?