Max failed logins– Please wait about 30 minutes and try again
You'd need to check your Brute Force restriction. They may be failing to login too many times. Or someone is trying to break into those accounts and triggering the restriction. WP Admin > s2Member > Restriction Options > Brute Force
You can also adjust that restriction to be less tight, but it'd still be important and good that you find why it's being triggered, especially if for so many accounts. Your server log may be helpful, ask your web host.