maybe when you got like 35 fragments you did the strike the blight minotaur appeared and somebody killed it, and you got it, and you dont recall it, that´s what happened to me, and i didnt knew, after you complete the full story it should be available to get, you´ve done the frame of the scout rifle? with 50 hadium and 50 weap parts? if not, i suggest you to continue with the TTK missions, and i think you should be doin good