I unfortunately, don't have the luxury of downgrading WinSCP however to address the issue, and am wondering if a solution was found, which didn't get added to the post above, because I see no updates to the article since 2020-03-27.
I've attached a WinSCP Log File that I generated (set to private), which includes the error described in the subject of this post. In my environment, we are using the latest version of WinSCP (v5.17.3 build 10325) to connect to the latest version of WingFTP Server (6.2.9) => https://www.wftpserver.com
For your awareness, I've also opened a "case" with the vendor for WingFTP Server to report this issue, which you may be able to reference here for additional information: https://bbs.wftpserver.com/viewtopic.php?f=2&t=3601
Let me know what other information you might benefit from having!