This issue has been added to the tracker:
https://winscp.net/tracker/1768
You can vote for it there.

Will see if other users face this issue as well.

martin wrote:

The only allowed positive response code to PWD command is 257. Your server violates the specification by using a code 250.

PWD
250 "/" is the current directory.

Thanks for reply.
So, maybe do just some option for this case and do not drop connection after received response code 250 and send
CWD / command as do other FTP clients?

The only allowed positive response code to PWD command is 257. Your server violates the specification by using a code 250.

PWD
250 "/" is the current directory.

See RFC 959:

Essentially because the PWD command returns the same type of
information as the successful MKD command, the successful PWD
command uses the 257 reply code as well.

Try to login a specific FTP-server. WinSCP cannot obtain current remote directory from
remote FTP-server. The log file attached to this message.