Based on our own and past user experiences, a lot of router manufacturers tend to bundle several features to beef up their product functionality, but most of which are poorly implemented and are negligent in updating their firmware to fix known bugs.
Very often the firmware that controls FTP & USB-over-LAN storage on such router devices are dreadful. This is by no means unusual - router (and NAS) manufacturers often use very old/buggy firmware code for these aspects, bundling such services just for advertisement sake that their products comes bundled with "additional features".
As a result, such devices very often refuses to store the Last Modification date/time values of files copied to it - which is one of the properties we rely on and check for to see if files on both sides are different or not. Instead, these devices stubbornly assigns current date & time of files copied, thereby never matching the LastMod date/time stamps of the files on your Source, resulting in repeatedly copied files from Source to Destination.
And unfortunately, there is nothing we can do on our end to change that (the refusal of the router's firmware to store correct date/time values, I mean).
Sounds like yours may have the same issues. If you try (for test purposes) using a USB drive that connects directly to your machine (and/or, to another PC you can access over the network) it is extremely likely the problems will disappear, demonstrating that it is the device you stopped using (router) is the cause of the problems.
Very often the firmware that controls FTP & USB-over-LAN storage on such router devices are dreadful. This is by no means unusual - router (and NAS) manufacturers often use very old/buggy firmware code for these aspects, bundling such services just for advertisement sake that their products comes bundled with "additional features".
As a result, such devices very often refuses to store the Last Modification date/time values of files copied to it - which is one of the properties we rely on and check for to see if files on both sides are different or not. Instead, these devices stubbornly assigns current date & time of files copied, thereby never matching the LastMod date/time stamps of the files on your Source, resulting in repeatedly copied files from Source to Destination.
And unfortunately, there is nothing we can do on our end to change that (the refusal of the router's firmware to store correct date/time values, I mean).
Sounds like yours may have the same issues. If you try (for test purposes) using a USB drive that connects directly to your machine (and/or, to another PC you can access over the network) it is extremely likely the problems will disappear, demonstrating that it is the device you stopped using (router) is the cause of the problems.