Not directly an answer to your question but I assembled a guide on restoring deleted notes which you could also use just to double check if your data is actually gone.
To check - you say that you "lost some notes" - do you mean that the entire note has gone or that changes made to a (still existing) note have been lost? The second case is the only one covered by the "in app" note revisions whereas the first requires somewhat more of a manual intervention (as per the guide).
As for backups, I honestly can't recommend the simple backup plugin enough.