I've been having this problem for the past 2 weeks getting my new commando up. I had 27 in my browser and no 28th. We'll, turns out I didn't do the objective meridian flashpoint part of the onslaught story. I quickly completed the solo flash point, went to queue veteran flashpoint, and I finally got credit! So make sure to do the onslaught campaign at least finishing the objective meridian solo flashpoint. You can't get the 28 flashpoint if you haven't completed the story mode objective meridian. Very strange but it fixed the problem for me.