The FileTransferProgressEventArgs.FileName contains a full path to the source file name. Not just a name. To it should be unique.

If not, tell us what version of WinSCP are you using and what protocol. A debug log file can be useful too (Session.DebugLogPath).

Would it be possible to return a unique Guid for each file being uploaded on the FileTransferProgress event.

Currently there is no way to distinguish for which file the progress is being reported (other than the file name, which is not unique enough). I am uploading files which are named the same, but reside in different folders.

This also gets tricky when there is multi-threading involved. I have 5 threads (for example) uploading files with the same name. I am unable to determine the progress for any given file.