Last updated: November 7, 2017
ISSUE
If you use OneNote 2016 for Mac and OneNote for iPhone and iPad, you may be asked to sign in any time you open the OneNote app or when you switch between notebooks. Similarly, OneNote may require you to sign in repeatedly to resolve sync errors.
STATUS: INVESTIGATING
Please update to the latest version of OneNote for Mac, iPhone and iPad. If you've downloaded OneNote from the Mac App Store, launch the App Store and check for Updates. You should see the option to update OneNote there. If you installed OneNote as part of Microsoft Office for Mac, then open OneNote, go to the Help > Check for Updates menu to launch the Microsoft AutoUpdate app and follow instructions there. Update all of the Microsoft Office applications, since they all use the same keychain items. To learn more, see Check for updates in OneNote 2016 for Mac.
To download the latest version of OneNote for iPhone and iPad, check the App Store for automatic updates. If you also have other Microsoft Office apps for iOS (Word, Excel, PowerPoint, Outlook), you will need to update all of them.
Mac mojave update. If you are still experiencing the issue after installing the recent updates, the next step would be to clear your Office credentials, and recreate them by following these steps:
To clear your Office credentials for macOS
Sometimes your credentials can get corrupted, causing OneNote to continually prompt you to enter your password. To clean this up, do the following: