Fileparts of large file download not getting reassembled

Hi Martin,

My compliments on an excellent product. My issue is that when downloading large files (1-4 TB) using SFTP, the transfer will proceed to the 100% point and then hang. I am using these features:

"Use multiple connections for single files" set to 9
"Download in background"
"Optimize connection buffer" is turned off

When I look at WinSCP in Task Manager, it doesn't appear to be doing anything--no CPU usage. I can see multiple large fileparts in the destination folder, but it seems like something went wrong during the reassembly.

The only way I have found to recover is to close WinSCP, reopen it and try to restart the download process. WinSCP will usually say that a file is in use, so I then close WinSCP and notice that the original WinSCP process is still running in Task Manager. If I end task, then restart the download, I get prompted to resume, and I do. The download seems to pick up from the point of the main filepart on a single connection. If I choose to move the download to the background, the secondary fileparts are deleted as new fileparts spawn. I have gone through the documentation, and I hope I am not missing anything obvious. I have attached the log. Thank you for your support.

I believe I figured this out. After looking at the log more carefully, I could see lines reading "[Background 2] Appending part 8 of "[filename].ext" to "[filename].ext.filepart"...

It looks like the fileparts were getting reassembled, but just slowly because they were so big. During the appending of the fileparts, the WinSCP.exe process appeared to not be doing anything (0-1% CPU) with the GUI showing the transfer at 100%. I should have read the log more carefully to see that the appending messages were occurring every 1.5 hours (fileparts were 500 GB each). I waited a couple of hours and another message appeared in the log, and one of the fileparts disappeared. I should have been more patient. It would be great if the GUI said something like "Appending filepart X of Y" so that it's easier to tell what's happening in the background. Thanks again for the great product and the great support.