Hi Cliff Gu MSFT,
Thank you for investigating this issue. Could you clarify what you mean by resetting the OneNote for Windows 10 application? Do you mean users should:
A. uninstall and reinstall this app or
B. sign out of this app (this removes the account), sign back in, and add the notebooks back in?
I have no problem with restarting the PC, but these resetting actions could be what's causing users more issues. In my case, my changes were all synced up, and I just had page sync error stating I should sign in. The sign in button performed no action. I did NOT make any edits after I saw the error, and when the fix came, everything was back to normal. Because my pages were all synced up with no further edits, my OneNote for Windows 10 app did NOT attempt to contact the server to bring in any changes. That's what I believe saved me -- I was able to at least view the page content despite the sync error, while some users could not even view their pages when the app tried to perform syncing actions. They got access errors. If you have edits that did not get synced to the server (you never know!) and try to reset the OneNote for Windows 10 app and add the notebook back in, you could lose all your edits. I would at least check that my changes are synced to the server by checking the page content on OneNote for Web before attempting resetting actions. Oftentimes, I need to perform browser page refresh multiple times to see my edits appearing on OneNote for Web (onenote.com site).
IMHO, without knowing what Microsoft development team has done to address this issue, it is better to wait a day before attempting any resetting actions. My husband told me that if a server is simply down, after it is brought up, people can see their apps working almost immediately, but if MS development team actually put in some fix (or maybe they took out the code that caused issues), he said it can take time to propagate those changes to all the servers in clusters and user groups. Also depending on which server the user's PC/app has the affinity to, some users may see the change before others, so he advised me to wait a day and save all my edits elsewhere (like Microsoft Word, Notepad, ...). I did NOT make any edits using OneNote for Windows 10, OneNote app (formerly called OneNote 2016), or OneNote for Web while the sync was broken because that could all cause synching actions on OneNote for Windows 10 and make the page not viewable.
You can also check out the messages from users Gwain96 and MuskrAAtz on the first page of this thread to see how resetting or editing (through another OneNote app like the web version) caused the page content to be not viewable on OneNote for Windows 10. If fix is on the way, IMO, the less action (resetting or editing) you take, the better off you are at recovering your page content and app.
This is a serious issue that makes OneNote for Windows 10 unusable, so please contact Microsoft development team and ask them on what caused this issue and also to advise the users instead of asking users to try expensive actions that could cause more harm. Please provide us update after you talk to the development team.
If some users still have issues after 1 - 2 days, at that point, they might have to perform some resetting actions, but personally I would not rush into that.