Symptom
Certain files are skipped while backing up OneDrive, showing the error "Cloud files are not supported", even when the appropriate permissions are set and files are syncing correctly.
Cause
This issue occurs because of inconsistencies in behaviour between different builds of Windows and different versions of OneDrive, and is therefore difficult to address broadly.
Solution
The following actions will increase the likelihood of successful OneDrive backups, but are unfortunately not guaranteed to solve the problem:
1. Check the Files On-Demand setting in OneDrive. This setting must be disabled for backups to work.
Note: After disabling this option, the OneDrive files will need to be rehydrated, which will take time. If a backup is attempted before rehydration is complete, you may still get errors.
2. Switch off VSS in ESE. (While this may help, we recognise that it is not an option for all customers.)
From 19.5, ESE will attempt to detect stubbed OneDrive files. If such a file is detected, an error "Cloud files not supported" will be logged and the file will be skipped. However, due to the same operating system inconsistencies mentioned above, this detection is not reliable.
Note: In versions of ESE older than 19.5, this error message will read "The media is write protected”.