If your members are attempting to login and recieve the error:
503 Service Temporarily Unavailable
This is caused when the IP restrictions of OptimizeMember are triggered.
You can modify these at: OptimizeMember > Restriction Options > Unique IP Access Restrictions
If you still experience issues...
If you still experience issues, it's possible that you or your visitors are accessing using an ISP which has a switching IP address system. This means that your IP address will regularly change and can cause issues with these IP restrictions.
To fix this, it is advisable to turn off these IP restriction options. You can do this by going to OptimizeMember > Restriction Options > Unique IP Access Restrictions and choosing the "Allow Infinite IPs" option from the dropdown menu
Ensure you click "Save All Changes" to save the settings