When using SNI SSL cPanel users can create SSL certificates using the main server IP address.
When a user doesn't have SNI support in their browser the default vhost's SSL details are shown in the error message.
In Apache the default vhost is the first one with that IP.
This means that the first customer's site in the httpd.conf file is shown as error message for all vhosts using the shared IP.
To fix this a default vhost needs to be created at the beginning of the httpd.conf file using the server's main SSL certificate.
This should be created by default when SNI is used on the shared IP address.