Microsoft has released OneNote Diagnostics Tool, a new tool that will help you diagnose OneNote problems & issues.
The OneNote Client Diagnostics Tool enables users to collect and send Diagnostics Logs from within OneNote to help the Support team when working with Customers on issues they are experiencing.
If the notebook that won’t sync is stored on OneDrive or on newer versions of SharePoint, try opening the notebook in OneNote for the web (at www.onenote.com). This can help determine if the problem is caused by the server or by OneNote.
In OneNote, click File > Info.
Right-click the URL shown below the name of the affected notebook, and click Copy.
In your Web browser, click inside the Address box, and then press Ctrl + V to paste the copied URL.
Press Enter to load the notebook in OneNote for the web.
If you’re able to successfully open the notebook in OneNote for the web and the changes appear, the problem may be caused by the desktop version of OneNote. Closing and re-opening the notebook there usually clears and successfully resets the connection. Follow these steps:
In OneNote, click File > Info.
Next to the name of the affected notebook, click Settings, and then click Close.
Switch back to the notebook in OneNote for the web in your browser, and then click Open in OneNote on the ribbon.