Gunsmith engrams that are rewarded every level is bugged, it only shows up if you revisit the tower. My gunsmith level is 13 and I have only realised this now, I think if you don't revisit the tower after some time/before you exit the game it disappears. I've missed around 10 rank up engrams since I have received at most 5 engrams from leveling. It's either this or not every level gives an engram and the description contradicts it which is a bug of its own, but this probably isn't it.