When installing RD Gateway Certificates using the server manager snapin. If the error ‘The WSMan provider host process did not return a proper response’ occurs. This error can be triggered by importing a PFX key bundle with no password.
The easiest way around it is to import the bundle into the local user store, then re-export with the password field set.
‘Certify the Web’ saves PFX files with no password. So if you are using a similar LetsEncrypt application to secure RD. This maybe your problem.