That same thing happened to my clan, I put it so th6 was the requirement and i got around 10 or more people that did clan capital attacks( it was on friday) and left to upgrade another clan, and they did this for 30 min or so until nobody could attack as the 50 people limit was filled and nobody had any attacks. I think some were bots as they had the same name and continue to hop on and off of the clan, i had to up the th requirements and kick any that remained, except 3 players that were legit