It's most likely because the file copied to your UNIX SFTP server does not have the correct Last Modification date/time stamp that matches your Source files, so SyncBackPro is proposing to re-copy them again.
Go to the following settings page:
Modify > Expert > FTP
and with FTP settings page opened, press F1 to review the information provided in SyncBackPro's Help file, especially Point 4 of the section under:
FTP Servers and File Dates and Times
for workarounds and other backup alternatives (Fast Backup).
Go to the following settings page:
Modify > Expert > FTP
and with FTP settings page opened, press F1 to review the information provided in SyncBackPro's Help file, especially Point 4 of the section under:
FTP Servers and File Dates and Times
for workarounds and other backup alternatives (Fast Backup).