Not sure yet whether this is a bug or just the way it worked in vanilla, but quivers are currently invisible to every player but the user wearing them. When the quiver appears on your character model as you shoot a bow or crossbow, it will not be visible on other player’s screens.
Would be nice to have some official confirmation from Blizz on whether this is a bug or intended! Personally, I think we should be able to show off our quivers as they’re a core part of the hunter fantasy.