Can you just keep the logging on and wait for the disconnect to eventually happen?
Before posting, please read how to report bug or request support effectively.
Bug reports without an attached log file are usually useless.
Please attach a full log file showing the problem (using the latest version of WinSCP) and some screenshots.
To generate log file, enable logging, log in to your server and do the operation and only the operation that causes the error. Submit the log with your post as an attachment. Note that passwords and passphrases not stored in the log. You may want to remove other data you consider sensitive though, such as host names, IP addresses, account names or file names (unless they are relevant to the problem). If you do not want to post the log publicly, you can mark the attachment as private.