ADFS configuration is quite a complex section in which one small mistake leads to hours of troubleshooting as well as its respective resolution.
We are facing some weird error while configuring the web application proxy in Windows Server 2012 R2:
Most probable cause would be: This issue occurs when finding DRS objects times out. The Active Directory Federation Services (AD FS) service tries to connect to every global catalog in the forest during DRS discovery. However, the DRS objects cannot be found because DRS is not initialized. Therefore, AD FS proxy times out.
But that didn’t resolves the issue in my case so I tried it from the scratch with the help of http://thesharepointfarm.com/2014/02/sharepoint-and-the-web-application-proxy-role/ - which resolves the issue for me but still didn’t clear as what went wrong!
Another step of troubleshooting that you can check is to check the certificates on ADFS Proxy.
If you have any further queries or questions then please let me know. I would be more than happy to help you as well resolves your issues J