There's one gym near me that I consider "my"gym, because it's high turnover and I can hit it easily before bed when I walk the dog, then I claim rewards from whatever gym I'm in. It almost never lasts 24 hours. Most gyms around here get prestiged up and hold on for a week or more, so it's nice to have one that anyone can get into at some point. But lately someone from Mystic with the name StratEVarious has been bubble stratting it and then a bunch of Mystic players will descend on it and fill the slots fast. The other day I saw it was level ten but only had three Mons in it, so I went in and started attacking. When my battle was over it was still level ten and had 8 mon in it. I saw a few cars and people walking, so it's possible it was legit... I can't be sure if there's any spoofing or multiple accounts going on, in fact I don't think there's much of it, but it's still frustrating. So I will spend whatever time it takes to ensure that gym goes down every night, hoping they'll give up on it after a while. But they do seem to do it more when the weather's bad, which often means it lasts two nights. I'd say rear them down and see what happens. If they're really cheating you may get a stronger clue.