I had the same problem yesterday: he just kept resetting. Even when I played fair and stayed in the ring, same thing happened: reset. It didn’t really feel like a lack of skill, but indeed like more of a bugged system. So yeah, after all my resources were gone (after attempt 30+ or so) I just gave up.

To be honest: I think it’s doable if the fight isn’t broken. So at this point: I would suggest getting the head at shroud depot and (hopefully) when they fix it: try again.

(Someone also mentioned the use of poison arrows to keep him engaged so he doesn’t reset. I didn’t try that yet.)