I had the same problem, but it fixed itself just by closing the game and trying again.
More specifically, the bug occurred after dying in the survival mode once, and then upon coming back whenever I picked up turret ammo it was invisible. I assume there was some kind of malfunction in the ammo coding that caused the game to hard reset upon entering the elevator.
More specifically, the bug occurred after dying in the survival mode once, and then upon coming back whenever I picked up turret ammo it was invisible. I assume there was some kind of malfunction in the ammo coding that caused the game to hard reset upon entering the elevator.