Entered floor 3 grift 55 solo as a ww barb (wastes + bk oath), killed a few mobs, boss spawned (Ember) who died almost immediately. As I was picking up stuff I noticed 2 bandits hitting me. Further investigation found that I couldn’t hit them. Dragged them away from Urshi so I could level my gems, ran into a 3rd bandit (also unhittable).
Not sure how they spawned or whether it was related to the boss dying; just reporting what happened.