My client has ArcGIS Portal and Server running behind their firewall and both web adaptors running on a DMZ server. There are secured feature services I need to access, but cannot reach because the login link doesn't work from the web adaptor. When clicked, it takes the user to a blank page and sits there. It doesn't time out or display an error. Unsecured resources are still accessible.
I've only noticed this behavior when using the web adaptor URL; I can still log in directly to the Portal instance.
I suspect either something went wrong when the web adaptor was configured or the firewall isn't configured correctly. I need help narrowing down the cause of the failure before I recommend any actions to my client's IT team, so any help would be greatly appreciated.