Assault Assignment Challenge 2 not progressing

Hi,

The assignement challenged for the assault class is not progressing in the task "Get kills or assists on concussed enemies" it got stuck on 11/15 since 1 month ago. I thought the updates will fix it but they didn't. The challenge cannot be re-rolled so it's stuck until something is done about it. 

I also have tried track and and played games where I got the accolation Stun assist or Stun Kill  but it didn't work. Also untrack the challenge and trye again didn't work. Retrack the challenge and retry didn't work either. I don't know what else to try, I would like to use the second variant of assault since looks useful and so people already use it, the disadvantage is there. 

I also tried verifying files in steam but no luck.

Please review.

Thanks.

Rafael.