Artifact weapon appearance

So I am doing the quest “The Arcway: Rite of the Captain.” I have to obtain the Eon Winder from Advisor Vandros in The Arcway on mythic difficulty. As well as two more quests which I already completed as the 2 other items dropped as they were meant to. The thing is, with this quest in The Arcway, I killed the final boss on mythic and the item that he was supposed to give me didn’t drop for me, I wasn’t even able to loot him matter of fact. I am trying to get this done tonight as I’ve grinded the nightfallen rep all day for this. Any suggestions?