“Duplicate Items: Some items from Bright Engrams can be acquired multiple times. Duplicates can be dismantled to provide the player with Glimmer and / or Legendary Shards. Other items, such as Emotes and Finishers, can only be acquired once because they unlock the access rights for the item on the player's account and can then be retrieved from the associated Collection.“ Until this season, shaders where like emotes and finishers, and only dropped once. There was dupe protection for those items, and at the start of the season it disappeared for some reason. I just hope it wasn’t intentional because I’ve got duplicates of the same two shaders from my last 4 engrams. (Edit: Misplaced quotation mark.)

I made no mention of whether or not shaders can/should drop, I merely pointed out that already having it is irrelevant.