Hi @Dom ,
- I suggest you change one network connection to have a check.
Besides, as the first notebooks is stored on OneDrive, you can check Service Health status page for any outages. If OneDrive is currently having issues, OneNote may be affected as well. - If change the network does not work, please go to "View Sync Status", if there is any error code or error message, please share with us.
- Then it's recommend to right-click the each URL shown on your image which start with "https://", and then click Copy.
In your web browser, click inside the Address box, and then press Ctrl + V on your keyboard to paste the copied URL.
Press Enter to open the notebook in OneNote for the web.
If the notebooks are opened normally, please compare the content of local notes with those in the cloud. - I also suggest you create a new notebook sync to OneDrive, to check whether the new notebook can synced successfully.
For more, please refer to "Fix issues when you can't sync OneNote".
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