Why are domains pointed to my shared IP showing the default webpage over HTTPS with ea-nginx installed?
When making a page request using HTTPS to the main Shared IP on your server, by default this will serve the vhost for the configured SSL/TLS Primary Domain. This behavior relies on the native functionality of the Apache web service. When a request is made to your server's shared IP over HTTPS, Apache will serve the top matching vhost in its configuration. The option 'Make Primary' in the WHM interface "Home »SSL/TLS »Manage SSL Hosts" is used to choose which vhost is placed at the top of the configuration.
When installing ea-nginx, this web service is acting as a reverse proxy in front of the Apache service and will instead decide which vhost to serve. Since the Nginx service configurations contain a default configuration for HTTPS that serves the hostname on the main Shared IP, any requests for domains that do not have an SSL installed on the server will be served through that vhost instead of the configured Primary Domain. As a result, you will no longer see the Primary Domain for the shared IP and instead see the Default Webpage displayed for unconfigured domains.
For more information, please visit the following resources.
How to set the default HTTPS vhost