How does local OneDrive determine if a local file needs to be updated?

Microsoft does not publicly document how the OneDrive client decides whether a local file needs to be updated. From observed behavior, the client relies mainly on cloud version IDs and cached metadata, not on continuous hash comparison. If a client fails to notice that a newer cloud version exists, it may treat an outdated local copy as current and upload it, silently overwriting newer changes. No conflict is generated.

Important points:

• “Always keep on this device” ≠ always up to date
• Timestamps and file size are only weak signals
• Hashes are not rechecked on every sync
• Sleep/wake, network changes, and long-open Excel files make this more likely
• This results in last-writer-wins data loss

This behavior is known but undocumented, and frontline Microsoft support cannot explain or change it.

Practical Workarounds / Mitigations

Before editing important files

• Pause and resume OneDrive sync
• Wait for “Up to date” status

For shared Excel files

• Use Excel co-authoring (open from SharePoint/OneDrive web)
• Avoid editing the same file on multiple machines offline
• Enforce “one editor at a time” for critical files

Reduce risk

• Enable and increase version history
• Avoid long-running open Excel sessions
• Avoid rapid edit-close-open cycles across devices

For critical workflows

• Treat OneDrive as distribution, not source of truth
• Use SharePoint, document management, or another system for authoritative storage

Bottom line

This is not user error. It’s a limitation of the OneDrive sync model.
If silent data loss is unacceptable, OneDrive sync alone is not sufficient.

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