Well this sucks, completed a quest last night that gave me an option of two different epic schematics. Upon completing I go and pick the one I want but then it lets me choose a second time which I thought was odd. So I choose the same one again and then it errors out on me and kicks me back to the home screen. I immediately log back in thinking it'll let me pick the weapon again but now the quest is gone and it's not under my completed tab either. Really really sucks to complete something only for the game to be like "fuck you" and erase my progress.
I had the exact same thing the other day. I pressed the feedback button, and told them, and a few days later found the first one in my inventory.
I could have sworn it was the schematic, and not just the gun, and all I got was the gun. Better than nothing, and maybe I was remembering the reward wrong.