My Book Essential 3TB stopped backups

The last automatic backup completed on 9/11/19. WD Backup will not create new backup even if I select ‘Backup Now’. It says it is preparing backup but does not write to disk. I have run diagnostics and get the following:

Drive status check- pass
Quick Drive test- stops at 90%
Complete drive test- pass

528 GB free space still available and accessible under File Explorer

Downloaded newest driver I could find 1.4.0.02 (2016). Had trouble installing because it said it could not install due to program running. Went to Task Manager turned it off and installed OK.

Rebooted several times.

Any suggestions?

thanks,