If a domain without a matching HTTPS vhost is requested, then Apache will serve the first entry in the configuration.
This typical issue is described here. Other times, users that have a website that requires functionality from clients which do not support SNI may also need to perform this modification, as this will allow non-SNI clients to reach the correct website.
To perform this change simply access the WHM.
WHM >> SSL/TLS >> Manage SSL Hosts
From here, locate the domain that you wish to be the first in the configuration and select the option called:
This will set this vhost as the first in the Vhost entries.