Challenge not unlocking

[Clanpred]

Am trying to get the gun butt kill challenge done. Am using melee with a recommended weapon.

For some reason I don't see the rifle being used when pressing melee. I see a knife at times or a foot kicking. However as I have been trying this for the weekly challenge I did see a reward for having killed 50 operators with gun butt but the weekly challenge remains locked.

yes I am using recommended weapons.

[Clanpred]

?