IWillMakeANoteOfThat

I've noticed similar issues happening where there don't seem to be any odd characters, so those remain a mystery. I used this site on the content of the "upload logs" embedded enml file to confirm there are no non-ASCII characters: https://pages.cs.wisc.edu/~markm/ascii.html I was able to test that it's content-related by making a copy of the note using the web interface and then deleting all the text from the original note-- it then uploads fine.

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 Event - Note[isLinked=false,contentClass=0] @ 285 15:37:18 Event - NOTE UPLOAD:: server error = BAD_DATA_FORMAT, NoteAttributes.contentClass note updated = 1570919544806 isLinked = false @ 285 15:37:18 The log also included a copy of the "enml" file, which is the Evernote internal XML. I checked that file for any odd tags and found nothing, however I did notice that the note contained a copy of Unicode non-breaking spaces instead of the usual spaces. Those were probably left over from a copy/paste at some point. It wouldn't surprise me if Microsoft Word were somehow involved, since it seems to really enjoy destroying perfectly good text. In any case, I made a copy of the note, replaced those non-breaking spaces with normal spaces, and was able to make the same edit on Android and successfully sync the note. So if you see that error, perhaps check your note for any odd Unicode characters-- it may save you some time and effort.

For plain text only notes, it's hard to beat the venerable pastebin. It makes a nice addition to Evernote as plaintext notes in pastebin can be added as links to an appropriate Evernote.