According to my last experience in a solo attempt in Dragon Star Arena (normal difficulty), I can confirm that something is wrong with targeting in the current version of the game. I was able to hit the Dark Mage with direct attacks in Round 7 without trouble with my stamina nightblade, but for a strange reason, I couldn't land a strike on the Black Knight with light attacks, nor heavy attacks, nor skills that focus single enemies like Blood Craze, Bloodthirst or Surprise Attack. I'm playing with the Oakensoul Ring and my best bet was to use the only area skill present in my bar (Barbed Trap) and do some kitting while the boss walked into the trap and survive as best as I could. Every time I tried to use a single-target skill, my stamina was consumed but the target didn't take any damage. Plus, there was no sound when my skills were used against this specific enemy.

A similar bug occurred when I fought the final boss of Naj Caldeesh with my sorcerer. Area attacks like Lightning Flood and Unnerving Boneyard (Yes, I'm using subclasses) worked properly against him but Destructive Clench and heavy attacks from my lightning staff couldn't trigger or do damage yet Destructive Clench cost me magicka when I attempted to use it. This is a bug that should be looked upon because it can be very counter productive and gamebreaking for groups that are used to do vet trials, trifectas or just discovering the dungeons recently added to the game. Even when playing casually, the exact same bug could happen again, like when I explored Deshaan and fought some Maulborn in the wild.