Shconfig.cfg (default setting shown below):
//How many days XP is saved after a users last connection
//Recommended max setting of 30 for VAULT style saving. Max value is 365.
If they don't play for 14 days their xp gets reset.
If you have a real problem this is not the place to post it, and please read the forums rules when posting in tech support so that you can supply us with the info needed to help you. And please do not reply to this.