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BugZero found this defect 1446 days ago.
A restore point created by Veeam Agent for Microsoft Windows appears to be missing files from a user's OneDrive folder. Upon further investigation, it is determined that Files On-Demand was enabled, and the missing files were in an Online-only state at the time of backup.
As a result of using Files On-Demand, files may become Online-only. The contents of a file in this state are not stored on disk, and as such, cannot be read by Veeam Agent for Microsoft Windows. Veeam Agent for Microsoft Windows does not interact with the files in such a way as to cause OneDrive to automatically download Online-only files. Files in the OneDrive folder in an Online-only state at the time of backup are silently skipped and are not available for restore from the resulting restore point.
Understanding OneDrive File States Only local files are able to read by Veeam Agent for Microsoft Windows. More information about file states can be found in Microsoft documentation here.
Files may be placed in an Online-only state when Files On-Demand is enabled in the OneDrive settings. Files in a OneDrive folder may be shifted to an Online-only state automatically if Storage Sense is enabled. The OneDrive File On-Demand feature may also be enabled by group policy. General information about syncing files with OneDrive Files on Demand is available here. Veeam Backup for Microsoft 365 - details and links