@Anonymous2: Did you try what I suggested above?

I downgraded version and now it works. Must be a bug

I guess the "unsupported protocol" indicates that your FTP server still uses a deprecated version of TLS protocol (1.0 or 1.1). WinSCP 6.3.1 has those disabled by default, as they are insecure.
You should urgently upgrade your FTP server.
Or, if you are willing to take the risk, you can enable these versions in WinSCP:
https://winscp.net/eng/docs/ui_login_tls

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If this does not help, please pot session logs from both versions.

I just upgraded WinSCP to version 6.3.1. and now cannot connect to an FTP site I need to use to transfer files. I get the following error message:

SSL3 alert write: fatal: protocol version
unsupported protocol
TLS connect: error in error
Can't establish TLS connection
Disconnected from server
Connection failed.

I'm running WinSCP on laptop running Windows 10. I can connect to the FTP site using another FTP client without any issues, using the same File protocol (FTP), Encryption (TLS/SSL Implicit encryption), host name, Port Number (990), Username and password.

Am I doing some thing wrong? WinSCP worked fine with earlier versions.

Thank you.
Ed Fritzen