The Content Discovery page is not being loaded when using HTTPS. The embedded iFrame src attribute is using HTTP instead of HTTPS
Content Hub uses the site's base_url so customer need to ensure that the variable is set correctly in the application to load it via HTTPS instead of HTTP.
The variable is $_GLOBAL['base_url'].
And if you notice that reverse_proxy_addresses is empty despite having set the base_url then it is because blt.settings.php is reinitializing $settings['reverse_proxy_addresses'] as per https://github.com/acquia/blt/blob/12.x/settings/blt.settings.php#L45.
Setting $trusted_reverse_proxy_ips instead propagated the values to $settings['reverse_proxy_addresses'].