RDS 2016 gateway error event id 312 "The user "abc@xyz.com", on client computer "xx.xx.xx.xx:2985", has initiated an outbound connection. This connection may not be authenticated yet."

When try to connect from public network to RDS 2016 environment web page is loaded, but when try to connect on RDP clinet, it will ask for credentials and after that it will connect to remote machine. Error shows as " your computer can't connect to the remote computer because remote desktop gateway server is temporarily unavailable"

When checking on error log found that even id 312 on gateway server

The user "abc@xyz.com", on client computer "xx.xx.xx.xx:2985", has initiated an outbound connection. This connection may not be authenticated yet.

I tried the registry key fix recommended for 2012 server (HKLM\SYSTEM\CurrentControlSet\Control\Lsa) and (HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\TerminalServerGateway\Config\Core) but no joy. It did not work for 2016 server. Please help.