How can I fix the OneNote notebook sync issue?

Back up any recent unsynced notes, then remove special characters—especially +, commas, #, and %—from every section and section-group name in the affected notebook and manually sync it.

1. Rename sections and section groups

This resolved the same 0xE0000644 9zu13 error in a closely matching Windows case where other notebooks synchronized normally.^1^

1. Before changing or closing anything, compare the desktop notebook with OneNote for the web.
2. Copy any recent desktop-only content into a separate, syncing notebook or another document. Microsoft warns that closing an incompletely synchronized notebook can lose unsynced changes.^2^
3. Expand all section groups, including nested groups.
4. Rename section and group names containing symbols. Use letters, numbers, spaces, hyphens, or underscores:
   • Projects + Ideas → Projects and Ideas
   • Sales, 2026 → Sales - 2026
5. In OneNote, select File → Info → View Sync Status.
6. Select Sync Now beside the affected notebook, or press Shift+F9.
7. Confirm that the error clears and that a small test edit appears in OneNote for the web.

The exact-code guidance also identifies problematic section or section-group names and local cache corruption as possible causes.^3^

2. If one section still fails

Identify the affected section under File → Info → View Sync Status; selecting the notebook’s yellow warning icon should show the section involved. Then rebuild only that section:

1. Create a new section in the same notebook with a simple name.
2. Right-click each page in the failing section and select Move or Copy.
3. Copy, rather than move, each page into the new section.
4. Press Shift+F9 and wait for synchronization to finish.
5. Verify the copied pages online.
6. Only after verification, delete the old section and optionally rename the replacement.

Microsoft documents this as the recovery method when an individual section stops synchronizing.^2^

Also inspect History → Notebook Recycle Bin. If it contains a damaged section, copy out anything needed and then delete that original section from the bin.^2^

3. Cache reset only if names and sections are not the issue

Clearing the cache forces OneNote to rebuild its local copy, so protect all unsynced content first:

1. In OneNote, select File → Options → Save & Backup → Back Up All Notebooks Now.
2. Confirm the backup completes.
3. Close OneNote completely.
4. Press Windows+R and enter:

      %localappdata%\Microsoft\OneNote\16.0
   

5. Open the cache folder and delete its contents.
6. Reopen OneNote and allow the notebook to download and synchronize fully.^3^

Do not sign out, uninstall OneNote, or remove accounts while unsynced notes remain; Microsoft warns that these actions can result in data loss.^2^

SharePoint-only fallback

If this notebook is stored in a SharePoint document library, ask the SharePoint administrator to check whether the library requires check-out, required metadata, versioning, or Information Rights Management. The exact error has also been reported where those library controls prevented OneNote uploads.^4^ If IRM must remain enabled, the documented Q&A resolution is to move the notebook to a library without IRM rather than weakening an intentional compliance setting.

References

1. OneNote can't sync one of my notebooks - code 9zu13 - Microsoft Q&A
2. [Windows](https://support.microsoft.com/onenote/onenote-help-and-learning/fix-issues-when-you-can-t-sync-onenote#notes-won't-sync)
3. Error code: 0xE0000644 9zu13 - Microsoft Q&A
4. OneNote sync error - Microsoft Q&A