A theft of Ivory, Tusks are not dropping.

I have killed the duo three times now. It drops loot, but the quest item "Tusks" are not dropping.

Tried resetting the instance. Tried logging out and logging back in.

Found the possible culprit of this bug. I was wearing the unique "The Devouring Diadem" and I suspect the unique effect of "Every 3 seconds, consume a nearby corpse to recover 20% of maximum life" is the reason the quest item didn't drop.

After 6 kills with no drop, unequipping the helmet and killing them one more time made the quest item drop.

I saw this bug the other day, and was also wearing the Devouring Diadem. I got the Tusks without issue after reloading and redoing it, but there are any number of possible explanations (such as, maybe I happened to have enough time before my next 3 second trigger for the Tusks to drop, maybe I happened to be standing far enough away that the corpse wasn’t targeted, maybe I used Lightning Warp to cull the mammoth which triggers different programming, etc.)