Backup completes, but files not present on Passport drive

I have had a 3TB WD Passport drive for a while - i setup a daily backup routine via the built-in software.

I see the daily notifications that the backup started and completed. But recently noticed that i do not see any updates on the drive - last files were written to the drive in July!

So i have been tracking every few days, and still: i get the Windows notifications about the backup start/end but no new files on the drive! I even deleted the backup plan and created a new one, and no go.

The drive is about half full (1.7TB free out of 2.72 TB)

What can the issue be? and more importantly- how can i fix this?