Ankur, there is also a Scheduled Job that runs in the background for every 15 min. Please check this code too. Even, this might cause the issue.

var userGR = new GlideRecord('sys_user');
userGR.addEncodedQuery("manager!=915dd5b80f3f52007b3a3e7ce1050e61");
userGR.addQuery('u_new_user_notification_sent', false);
userGR.addNotNullQuery('manager');
userGR.addNotNullQuery('u_start_date');
userGR.addEncodedQuery('active=true^sys_created_onONToday@javascript:gs.beginningOfToday()@javascript:gs.endOfToday()^u_start_dateRELATIVELT@dayofweek@ahead@3^ORu_start_dateRELATIVEGT@dayofweek@ahead@28');
//userGR.addQuery('u_start_date', '>=', gs.daysAgoStart(3));
//userGR.addQuery('sys_created_on', '=', gs.daysAgoStart(1));
userGR.query();

while(userGR.next()) {
    var cart = new Cart();
    var item = cart.addItem('0cbbe496db880c10db945a48dc96193a');
    cart.setVariable(item, 'name', userGR.name);
    cart.setVariable(item, 'support_group', userGR.u_support_group);
    cart.setVariable(item, 'requested_for', userGR.sys_id);
    cart.setVariable(item, 'location', userGR.location);
    cart.setVariable(item, 'division', userGR.u_division);
    cart.setVariable(item, 'email', userGR.email);
    cart.setVariable(item, 'start_date', userGR.u_start_date);
    cart.update();
    var rc = cart.placeOrder();
   
    userGR.setValue('u_new_user_notification_sent', true);
    userGR.update();
}