Hello @molivos
Have you reviewed:
Security History → Cloud Backup → Advanced details here … review → # files failed to back up
Advanced details = click
for example: 7 files failed to back up
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When I had Backup sync failed.
My backup set was trying to back up System Volume Information
~ my Cloud Backup set tried/failed to back up System Volume Information apparently because I had opted Back up common file types only = off.
System Volume Information folder contains hidden protected operating system files.
I’ve since excluded System Volume Information folder.
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Hello @molivos
Have you deleted your backup sets online?
User may opt Reset to Default…to start over…if you want.
Settings → Troubleshooting → Reset to Default
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Please post progress