Noticed similar with the lfg group yesterday. Got them to gatekeeper without any issues, but then the same guy would die to the Wyvern every single time, would not take advice on how to maybe not do that, or what loadouts might help him. Then came atheon. Wipe after wipe with all but one in the team having <300k damage after two rounds. After a couple of hours we called it. I joined an Atheon cp with 3 that had gone through the same thing, then 2 joined with same story. Took a few tries and he was done.