I hear you.
The back-up program from the Western Digital drive I had needed to be uninstalled completely to stop the shenanigans. Even turned off, there was still a piece of it that would check the files to see if they changed, it just wouldn't write them to the back-up drive. Apparently, it was a feature of the program. So it would know which files it hadn't backed up, that way when you turned it back on, it would get those first.