Arena of the Slakhanan issues?

I've got this strange issue in one of my mods (and I'm trying to figure out what is causing it), where in the Arena of Slakhanan, I am unable to complete it.

The game simply drops out after the first round and I'm left with a white scroll option, with an objective: defeat the troll warrior. Only he's been defeated. Normally when you click on a quest, it pops to the location but in this case, it seems bugged.

Any idea what could be causing this type of bug?