MTAR-21 Locked after Completing the Challenge

A long while ago, I completed the Multi-Talent assignment, and had unlocked the gun. It eventually became one of my favorite guns totaling to this day 600+ kills. Last week I had tried to use it, but I had noticed that it was locked. I tried to complete Multi-Talent again, but it says "Complete." I can no longer unlock, use, or even pick up a kit with the MTAR in it.

I am unsure whether something like the Carbine Shortcut Kit would unlock it, but I don't want to buy it because I have unlocked every carbine.

Any help would be appreciated, and for future notice I have already talked to a Battlefield support agent; case # 18274615.