Same issue, started recently. I created a note in the iOS app, after the app is closed and then reopened, the note is gone (not to be found in trash, completely gone!). Tried a bunch of scenarios even open closing the note several times to ensure it did exist. I'm running the most current version of the iOS app.
This alas is a dealbreaker, Evernote. I fear this is the end of our relationship of five plus years. 😔