If there is a fly booster players do /fly and with theirs hack enable the fly hack they can fly cause i see alot of players fly at spawn i am not sure if this can be fixed but do a try to fix it.
Probably the most people where you are talking about, have a rank. And those ranks give them the ability to fly.
You aren't allowed to fly at spawn, even with a rank, only the player-admins have this permission (and above ofc.) So whether they are titan or member, you can't fly at spawn