What are the blood ghosts attacking me?

I apologize if this has been asked an answered but I’ve search and not found this info.
I’m a returning player on seasonal character, S16 I think?
At some points after a fight and I’ve cleared all enemies on screen, I get attacked by 2-3 enemies I can only describe as blood ghosts. They appear to be actual in game enemies but transparent and shimmery and red. They have no names, no health bars, and I can’t attack them, but they attack and damage me for a few hits and then they disappear. So far I’ve seen skeletons, bandits and quill rats appear in this form. It seems to be a rare occurrence and I don’t know how to make it happen to predict it and take a screenshot.
I’ve seen posts about unknown ghosts appearing from some class abilities so for your information I’m a necromancer with Reap, Blood Lance, Corpse Explosion, Blood Mist, Decrepify and Blood Wave, all modified as blood skills.
But I assume it’s not a graphic from any of my skills because after the battle they hand around and damage me.

Is it just a game feature for some lore reason I have to put up with or is there a way to kill them?