Re: New issues: turning off 'Optimize connection buffer size'
Try to add
https://winscp.net/eng/docs/message_host_is_not_communicating
https://winscp.net/eng/docs/rawsettings
-rawsettings SendBuf=0
to the open
command.
https://winscp.net/eng/docs/message_host_is_not_communicating
https://winscp.net/eng/docs/rawsettings