We recently came across a strange situation where we could not add sections to an existing OneNote notebook hosted in SharePoint 2013.
Using the Web App we noticed that the New Section option under Insert was grayed out. Also we noticed we could no longer sync the notebook from a local copy of OneNote 2013 to the file in SharePoint.
I could open the notebook locally and can interact with it fully locally but when I synced the notebook to SharePoint, none of the changes get reflected in the Web app even though OneNote says it completed the sync successfully.
Up to this point I had been trying to open the Notebook using the automatically generated link the Quick Links area of the site. Instead I went directly to the Asset Library of the site where the OneNote file is hosted and opened it.
I could see the sections and also saw the parts that I had created locally and synced. It was strange.
Looking at the URL for the quick link:
http://web.local/Departments/IS/USA/_layouts/15/WopiFrame.aspx?sourcedoc=/Departments/IS/USA/SiteAssets/USA IS Meeting 2013 Notebook/Myrtle Beach, SC Notes 2013.one&action=default
versus the direct link from the library:
http://web.local/Departments/IS/USA/SiteAssets/USA%20IS%20Meeting%202013%20Notebook?Web=1
It looks like for some reason the quick link was configured to only open one specific section and not the entire notebook. That explains why I could not add additional sections and why I could not see what I was syncing, because I was not actually opening the whole notebook. Only that one section.
The solution was to edit the Notebook link so it used the direct link. Problem solved.