I restart playing again in Season of the Splicer, and wanted some of the Season of the chosen weapons, so I played Battlegrounds, but after 50 clears and some Umbral Engrams, Threaded Needle and Brass Attacks won't drop neither "Near and Deadly", "Eplosion and Detonation" engrams. I have most of the triumphs and all seasonal challenges from season of the chosen related to battlegrounds. I really don't know if its a really bad RNG or some bug with not been able to drop Season Pass Weapons, even so I have the Deluxe.