I have a My Book that I have been using successfully for over a year. I do not always leave it connected to my computer in case of ransomware, instead connecting it about once a week and kicking off a WD Backup, which would end successfully. Checking recent, my last backup to restore was seven months ago. I tried various things, including shutting down my computer and My Book, and upgrading from the older WD Backup version (1.5-) to the current 1.9-. This includes just after a reboot with no applications running. I have run the WB diagnostic tools, and it gives My Book a clean bill of health.
I was able to get one backup to run, which had a lot of files it reported that it could not backup, and now it’s returned to the bad behavior both from schedule or manual backups. I do not have excessively long or deep directories, many of the skipped files were on the Desktop or one level down off My Documents.
The behavior when it is not working is WD Backup shows Preparing Backup, spins for a bit over 6 minutes, and then reports backup successful. The current date is not added to Restore Files tab and I can confirm that new/changed files have not been backed up by browsing My Book.
I have a 1TB internal HD (50GB free) I am attempting to back up to a 4TB (1.95TB free) My Book. I am running fully upgraded Windows 10 64-bit, and the most current version of WD Backup.