Having played a few rounds of campaign this weekend, I noticed that twice a slot for one of the rewards for completion was instead glitched out, and provided no reward. I've got a picture attached (Fourth item on the list in this case), but unfortunately, I can't seem to find what causes it. Once was the reward from Fort Romor, and I believe the other was just a normal AZ1 pack. Both times I got the glitch, I happened to be using Mercenaries (Oni and G24A-19), but I'm not certain if that's a coincidence or a cause.
Never shift in to reverse without a backup plan.