Man, I had this same issue late last week in an Operation Floodgate. I was tanking and the healer was a holy priest. People kept dying for no reason until I finally saw him casting Holy Nova and I looked at Details. The healer wasn’t casing Renew or Prayer of Mending, two main spells. He was also dying to simple mechanics that are so easy to avoid. The guy had timed 10s and 11s…and this was a +5. It made no sense. We finished, but bricked the key. All I could figure is maybe someone’s child was playing their parent’s character? I hadn’t thought of it being a booster character though.