Oh, well, yes - it looks like the SSH server cannot access those files.
Sorry then - and thanks for the great software :-)
Do you think there's a problem on WinSCP side? Can you access the path using any other SFTP client? If you can, please post logs both from WinSCP and the other client.
when the remote box is SSH running on Windows (default OpenSSH of Windows 10) it would be really useful to access a path inside a WSL distribution - this would be \\wsl$\Debian (from Explorer), or could be //wsl$/Debian
Currently this is refused with failure code 4