The behavior described suggests two separate needs: stopping the random loss of pages going forward, and recovering work when it happens.
To protect current and future work:
- Confirm where the document is stored
- If the file is stored in OneDrive or SharePoint, AutoSave continuously writes changes to the cloud copy. This is the most reliable setup for avoiding data loss and for using Version History.
- If the file is stored only on the local disk or a network share, Word relies on AutoRecover instead of cloud AutoSave. In that case, configure AutoRecover as below.
- Turn on and tighten AutoRecover
- In Word, go to File > Options > Save.
- Ensure Save AutoRecover information every x minutes is checked.
- Set the interval to a small value such as 5 minutes or less so that at most a few minutes of work are at risk.
- Ensure Keep the last autorecovered version if I close without saving is checked.
- Keep using AutoSave when working in OneDrive/SharePoint
- For documents opened from OneDrive or SharePoint, leave AutoSave set to On so changes are continuously saved to the cloud document.
- Use Version History instead of restoring very old copies
- If the file is in OneDrive or SharePoint, use Version History to go back only as far as needed instead of days or weeks:
- Open the document in Word.
- Select File > Info.
- Select Version History (if available).
- In the Version History pane, open recent versions until finding one just before the unwanted deletion.
- Select Restore on that version to roll back without going back to very old states.
- If large sections disappear again
- Immediately check File > Info > Version History (for cloud files) to see if a recent version still contains the missing pages.
- If the file is local, after a crash or unexpected closure, look for the Document Recovery pane when reopening Word and choose the most recent recovered version.
These steps do not explain why the deletion occurs, but they ensure that when it does, recovery is limited to minutes of work instead of days, and that the correct recent version can be restored instead of rolling back to much older copies.
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