What does it take to unlock co-op milestone weapons?

Seriously, I've googled this. I had this issue over a year ago and quit and its still present. To unlock the E-11D you need 50 kills as the assault class in co-op. Well. 5 games later I am at 3/50. Just ended the previous one one a 32 kill streak. What the hell does this take? Other weapon unlocks are progressing but not these. How hard is it to fix this bug?