I have a note created on Evernote for Windows, to which I made a trivial edit on Android and immediately the note failed to sync and went read-only so I couldn't even edit and try again.
In the process of creating a support case for Evernote, I enabled single-note error log uploads and created a log for this note. Within that single-note log I found this gem of an error message:
Event - Note[isLinked=false,contentClass=0] @ 285 15:40:18
Event - NOTE UPLOAD:: server error = BAD_DATA_FORMAT, NoteAttributes.contentClass note updated = 1570919544806 isLinked = false @ 285 15:40:18
Ev