Thanks for your reports. I have added this to the list of know false positives.
https://winscp.net/tracker/530
Unfortunately it does not seem like I can report the false positive to Yomi Hunter.

same here
Virus Alert!
The requested file 'WinSCP-5.15.9-Setup.exe' has been blocked.
Block Reason: Barracuda ATP
Threat: Risk estimate: Medium Risk - Sample contains suspicious behavior.
Details: Barracuda Advanced Thread Protection found an APT
URL: https://winscp.net/download/WinSCP-5.15.9-Setup.exe

Virustotal is flagging winscp.net as malware with one engine, Quttera. I have downloaded winscp version 5.15.9 and uploaded the file and the sandboxing site Yomi Hunter is flagging it as malware. I do not see this with the previous version 5.15. I assume that this is a false positive, but it was definitely flagged in our normal scanning procedure.