One of the issues I ran into this week involved Windows Server Essentials 2016, and the websites it creates as part of the Essentials role in IIS. All of which started returning an HTTP Error 501.19. This can also manifest as the connector software failing to connect, with the error "Cannot get information from 'servername'. Please contact your system administrator."
This also coincided with WSUS being temporarily installed and removed from the server for unrelated testing. It seems however that removing the WSUS role doesn't quite put the IIS configuration back to how the Essentials role sets it up, annoyingly the repair tool also fails to repair it.
Checking the file structure and permissions seemed to reveal nothing unusual, upon checking the IIS config however it looks like WSUS turns on Xpress HTTP compression, which in turn seems to break many if not all of the Essentials features. Running the following command on the server will remove it from IIS config, and after restarting IIS the Essentials roles are working properly again.
%windir%\system32\inetsrv\appcmd.exe set config -section:system.webServer/httpCompression /-[name='xpress']