I'm killing them with my fists (not takedown) and its not registering. Also this weekly event reached the midway progress and i did not get xp, so i think i'm still not participating/in the event. I enabled it but the progress bar is not moving.
Make sure you don't have a gun in hand when you are killing them. I did buy brass knuckles at the end, but I think the real issue was the gun in hand. Equip only fists so they show as fists on screen and then go punching. I used Fast potion and Furious potion to quickly get to them and one shot them.....I also added brass knuckles to this.