Weapon not unlocked

I have the problem with the KTS100 MK8. ​​I completed the challenge, but it's locked. Then I did the challenge for the second LMG, and I can equip that one. I tried re-doing the challenges from the first challenge, but that didn't work either. I even uninstalled the game, but that didn't help either. Now, thanks to Redsec, I've leveled the KTS to 10 and unlocked the War Operations variant, and I can equip that one, but I can't change any attachments, and the regular KTS is still locked. Fix your game!