Are Windows 10/Android OneNote files no longer compatible with OneNote 2010?

Alright!  The fix has been deployed server-side to stop generating content incompatible with OneNote 2010.  New pages/sections created in OneNote for Windows 10 will now sync properly to OneNote 2010.  So it's safe to use OneNote Win10 again.

Unfortunately, the existing content is already broken in OneNote 2010 :(

The easiest workaround is to run OneNote 2016 which understands the format change.  We have a free version compatible with OneDrive:

http://www.onenote.com/download

The free version has a few limitations, such as no local notebooks, but since you all are using OneDrive already this may not be an issue.  Although some of you have reported these are work devices, so I don't know if you're allowed to install OneNote 2016 onto these devices (might be blocked by IT admins).

To get this working again in OneNote 2010, unfortunately you need to copy the content within OneNote for Windows 10 to regenerate it.  This can be a cumbersome process...  If it's just a few pages, right-click those pages in OneNote Win10 > Move/Copy > Copy into the same section, then delete the old page.  Page copy + delete will be the most reliable.

If lots of pages are broken, or the entire section is broken, you can right-click the section > Move/Copy > Copy into the same notebook.  This copy will append a "2" to the name since sections can't have duplicate names ("Quick Notes" copies to "Quick Notes 2").  New section sync can be slow, and rename can be flaky: it's best to right-click the notebook and Sync This Notebook (or Shift+F9) to force it to sync.  Once 2010 sees the new section, then you can delete the old one, and again force it to sync.  Once the delete finishes syncing, it's then safe to rename it to remove the "2" appended to the copy.

I apologize for this tedious workaround :(