I've done it three times now and the boss still drops nothing at all. I was hoping to get a motif.
Is this a bug or is it just very rare to get loot? I'm definitely doing my part during the fight.
If the boss doesn't light up and provide loot it is most likely that you are being out DPSed. If there are a lot of people in the arena with you, then this is a good possibility. Even if you are contributing.