Basically title. Quickplay cataclysm enchanter’s lair, we entered the final boss fight. Upon Nurgloth starting the onion ring slam phase (NOT while he was standing up on his dias invincible) I walked up to him and headshot him with the double shot Bounty Hunter ultimate. The headshot noise played for both shots, and the cooldown reduction on headshot also applied.
However, he seemed to take little to no damage and the armor icon appeared below my reticule as though the ultimate had somehow been blocked. This is despite the fact that he was doing his onion ring slam phase and seemed to be taking normal damage from other sources, such as my repeater pistol. I cannot confirm whether this happened to every instance of my ult during the fight but it happened at least 3x consecutively during the scenario mentioned above.