If subdomain isolation is turned off, you should also disable GitHub Enterprise Pages to protect yourself from potential security vulnerabilities.
Setting GitHub Enterprise Pages to be publicly accessible
If private mode is enabled on your instance, GitHub Enterprise Pages are not accessible to the public. You can configure GitHub Enterprise Pages to always be publically accessible.
Warning: This is an instance-wide setting, meaning that every GitHub Enterprise Pages site in every repository will be public.
At the top of the Management Console, click Settings.
In the left sidebar, click Pages.
Select Public Pages.
Disabling GitHub Enterprise Pages
At the top of the Management Console, click Settings.
In the left sidebar, click Pages.
Unselect Enable Pages.