You should probably use some kind of versioning so that when you receive version 123 and the version in the database is 121, you won't commit 123 until you receive #122.

If the user deletes the note and the server receives the delete request before other modification deltas, simply ignore the deltas that arrive after the delete command.

In my opinion it's a lot more simple to solve this kind of problems on the server side of a web application.