During Legion artifact quests, some mobs in various Legion Artifact quests are showing up as “skull” level and are impossible to handle. These are mobs that should be a normal non-elite level 40, as well as elite mobs. It’s clearly a bug. I am doing these quests on various level 50 toons (post-squish, Jan 2022) that pretty much lay waste to other mobs in the Legion zones.
Other people are posting the same thing on Wowhead and other forums, I’d be surprised if someone hasn’t posted here about it.
Edit: Looks like it’s not simply artifact quests. Quests that appear to have phasing involved - I was doing The Reluctant Queen and the three assassins that ambushed us were all “skull”-level. They pretty much kicked our teeth in, though I was able to bubble and hearth when they aggroed as I was recovering my corpse.
Edit, next day: Hit level 51 on the Paladin I’ve been playing in Legion. Went back to Val’sharah, the mobs are a mix of grey 45s and red 60s.