To Fix:

Please check both URL:

https://www.experts-exchange.com/questions/29098816/URGENT-Windows-10-April-2018-Update-broke-RDP-credentials-to-Remote-Desktop-server.html

https://www.windowslatest.com/2018/05/09/windows-10-kb4103721-bugs/

https://superuser.com/a/1321419

Try checking both fix and it should start working.

Regards