If people have lost access to the Content Library in a Staff Notebook or Class Notebook you’re the owner of, visit the Fix notebooks page on OneNote.com. Select Fix Permissions beside the notebook people are having trouble with. When you see Permissions Fixed, they should have access again.
To help avoid this problem in the future, we recommend installing these updates:
Note: OneNote for Windows 10 doesn't require these updates.
Why this happens: Content Library has special read-only permissions. When the permissions get interrupted (like when a read-only section group is moved) Class and Staff Notebooks protect themselves by automatically locking down the Content Library so that it’s only visible to the owner, and nobody else.
When this happens, everything is still in your Content Library. While it’s locked down, staff members and students can’t see it.