Hey there!
As Varnish is not software we support at cPanel, I am limited in regards to what information I can provide. Default page errors like this occur when there is a disconnect between a request being received in a browser and the Apache webserver. The most common cause is an IP mismatch; where the IP address assigned to a domain in the Apache configuration differs from the IP address the domain is pointing to at the DNS level. Or, the domain simply doesn't exist on the server.
There could also be an issue with how the Apache ports are assigned in the virtual host configuration, considering you moved the Apache port to 8080.
We have an article written that should help you in troubleshooting this default page issue.
Sometimes, when you load a site it will load a default cPanel page. When you access the server's main IP address on port 80, it displays the default page, since by default, there are no IP-based Vi...
support.cpanel.net
Don't hesitate to reach out if you have more questions!