Strange potential Soul Eater rare bug in delve

I was watching my friend in Delve the other day and he encountered a Soul Eater rare that for whatever reason was not taking damage, no regen or damage reduction mods were present. I thought it was just a weird bug initially, I started delving myself and ended up encountering the same issue. Soul eater rare that was not taking damage, in fact it wasn't even registering my hits as fortify and cruelty weren't proccing. I have since encountered this issue myself at least five times, and every single time it was a Soul Eater rare with one of the elemental trail modifiers and nothing else, just two mods. My friend has also started paying attention to this and has noted the same.

It is 100% not an issue with darkness or something because its always been on the end node where typically darkness isn't an issue (also threw flares just to be safe).

Just happened to me as well. Soul eater + trail of fire and it would not die

I had this crap happen to me maybe like a week ago in delve. It seemed like mob didn't do any damage (I think?) but it wasn't dying also... WTF.

I was standing there hitting it for maybe like a minute just out of curiosity, but nope, the mob bugged out or whatever.

Who knows, new league new bugs in PoE I guess.