Originally Posted by
Zenion
Alright, there's your problem. You actually get the fourth ID tag for completing all 50 assaults at least once, not for reaching Captain; if you don't have that, then you missed one somehow. Captain rank requires you to have completed each unique assault (except Nyzul Isle ones, which don't count for this) at least once, no getting past it by repeating an easy one a few extra times. Double-check in Missions > Assault to see which ones you're missing, and follow up on those. That should get you back on track.