Also maps can be the reason for this. Also players low internet connection.
I'm sure you do not have that much bad plugin that can cause this overflow.
I make one simple test:
Take this plugin
https://forums.alliedmods.net/showthread.php?p=422732
and set this cvars:amx_ssinterval 0.1 and amx_maxscreens 99999999
And with that low interval player still can play a few minutes without owerflow.
Some players are get owerflow after few seconds,some 5-10 minutes.
The biggest problem here is internet connection of the players and maybe rate stuff.