This is the expected behavior of the form when Save & Continue mode is enabled. Users would be able to save records and these records would show up in Airtable as soon as the first save operation occurs. This will not create multiple records per submission, as each record that is created is simply updated after the initial save.
No formula can be calculated on the miniExtensions Form itself without creating a record in Airtable first.
You can learn more about Save & Continue mode in this help article: How does Save and Continue work?