Rathbreaker reset, stopped attacking

In the middle of the Rathbreaker fight, he suddenly ran back to his starting location and just stopped attacking. He could be damaged but his regen was way too fast, and I couldn't kill him.

Tried logging to character select and coming back, he's still standing in the same spot, didn't initiate the fight. Tried exiting the game and relogging, same thing. Had to go play a druid for a while (maybe an hour I played) and come back and it worked.

Not a huge deal but thought I should report it.