Guess who just unequipped cluster grenades! This guy!
Guess who just unequipped cluster grenades! This guy!
I am pretty sure the Cluster Grenade makes your damage 0 in results screen for both Arkfal and Co-Op missions. I haven't tried this after the patch but if you are still bringing it up then it must still be true.
For what it's worth, I've never used cluster grenades but I have been hit with the zero damage bug.