In Act IV Hell difficulty, I found a pack of champion Vampiric (something else) (something else) Corrupted Angels. My attacks were only hitting them for 1500-2000 when normally my hits are in the 5000-6000 range. I was using a physical-only weapon.
After several tries I realized that I could not kill them, no matter what I tried. The vampiric healing was more than enough to outdo my wimpy hits.
I started paying attention and noticed that the normal Corrupted Angels were only taking about one third of the normal damage as well. I don't think it was a debuff, since I alternated hits against an Angel and then a different mob and could clearly see the difference: 2000, 6000, 2000, 6000, etc.
In a later run I didn't see this behavior at all. I noticed I had changed to a fire-based weapon.
Is there some sort of hidden physical damage resistance that corrupted angels have?