Mercenary healing enemies

SO I got this op mercenary with holy relic and consecrated path, and lately as i got into t16s (and my damage isnt at the point where i can kill bosses quick enough), I have been noticing the map bosses regenerating life/healing ALOT.
Literally outhealing my damage. In all the cases where this happened none of my map modifiers had anything that would allow or make the bosses heal or regen. Even less this much.
I believe the mercenary is healing them. If someone has some insight on this please let me know.
Thank you.

not sure if similar but I wanted to make my own bug post about an enemy all of a sudden healing a lot/outhealing my possible dmg. It wasn't in endgame but the new act 4, Kaom's Test of Mettle rare enemy. Thought it was maybe a mechanic of the trial at first but probably a bug. I was playing not mercenary, but Amazon Huntress, wielding quarterstaff. The modifiers of the rare enemy in question didn't have anything to do with healing, but off and on it would just activate Dr. Mundo ultimate and heal to full and I couldn't deal any damage.