After adding a new IP address to the server, or validating the existing primary IP address using the mainipcheck script, the server's primary IP changes to a secondary IP.
This is caused by adding a new IP address with an incorrect netmask. An invalid netmask can cause the primary IP to fail resolution checks, which prevents it from being used as the server's main IP.
Remove the new IP address, and ensure you are adding it with the correct netmask. You may wish to double-check with your hosting provider or data center to ensure you have been given the most accurate IP information.