The anti-cheat works partially by monitoring packetloss, if too many packets are dropped between the server and a client, the anti-cheat will assume they have alt/tabbed out of game to turn on a hack or something, and kick them. Although this is probably not the case, since you're hosting the server on your home Internet connection there will most likely be packetless because of the small amount of available bandwidth.
As for the join flood, there's no way to change that.