SFTP Problem: "1 requests to fill 1 data gaps were issued"

I have a scheduled task that runs each day at the same time to transfer a file from an SFTP site using WinSCP Portable version 5.1.5. The files are SQL Server .bak files (.bak). Most days the transfer completes successfully. But maybe once a week, the file appears to transfer correctly, but the transferred file is not a valid SQL Server backup file, and were I to try to restore it to SQL Server, the restore would fail. If I begin the job again later to transfer the file, it will work--i.e. I will have a valid SQL Server backup file that I can restore to SQL Server. Attached are (what I believe to be) the relevant part the logs from 1) a transfer that works correctly and 2) a transfer that does not work correctly. Can anyone shed some light on what might be the problem? Thanks.

Are you sure that the file was not being written to, while you were downloading it? The message (from subject) would indicate that.

martin wrote:

Are you sure that the file was not being written to, while you were downloading it? The message (from subject) would indicate that.

Thank you. It is possible that the file is still being written to. If my understanding is correct, I can only see the time stamp indicating when the file began being written to and not when it finished being written to. To me it seems like I'm allowing more than enough time for this particular file to be written before I start transferring it, but perhaps not. I just didn't know if the message in the log, "1 request to fill 1 data gaps were issued", could indicate some other problem than this. So thank you for this confirmation.