Error saving file on tunneled connection

I have set up a connection through a SSH tunnel with WinSCP 5.19, using local tunnel port 50002.
Whenever I open a file using internal or external editor and try to save it, I get the following error:

Error while tunneling the connection.

Local port 50002 forwarding to 192.168.1.100:22 failed: Network error:
Address already in use

Can you help, thanks!

You actually cannot fix the tunnel port number, if you want to use the background transfers (needed for editing). Keep the Autoselect option.

The next version of WinSCP will handle this better:
https://winscp.net/tracker/1996