I have also been having this problem for the last year or so. The android app allows you to edit the note without touching the edit symbol. I don't think that's the answer because some notes would save and sync correctly and some got locked. In many cases all I did was correct the title of the note or add tags. Those changes also cause locks to happen. Now, I try to make sure I touch the edit symbol even if I'm not changing the body of the note. It seems to help. I forgot on one note yesterday and it locked. But when I went to fix it today, it no longer shows as locked. So, that's weird.
I did report the locking problem to tech support last year but the response wasn't very helpful. I don't remember exactly but it boiled down to make a new note and get rid of the old one.
However, the biggest problem I have right now is: How can I find the locked notes amongst the thousands of notes in my Evernote? When running the sync, it dings and shows which note fails but they go by too fast to make note of. The notification only mentions one note and when you click on it, Evernote just shows some generic text about making sure you're the owner, etc. - doesn't take you to that note. There doesn't seem to be a way to view a log showing the failures. So, the only way I know to find them is to sync, capture the title of one note, fix it, repeat until they're all gone.