I had somehow got the arena master as a quest giver, and went into the arena after talking to him. I died very quickly as I was fighting alone. At that point the mobs stopped spawning. I decided to abandon the quest to reset it, thinking I could just go talk to the arena master again. Well I was wrong, he was no longer interested in giving me the quest. I don't know how he got marked as a quest giver in the first place.