This is the expected behavior of the form when Save & Continue mode (formerly known as Compute Mode) is enabled. Users would be able to save (or compute) records and these records would show up in Airtable, but users will not be able to confirm these records unless they click again to submit.
No formula can be calculated on miniExtensions Form itself without creating a record in Airtable first.
For more information about how formula fields work in miniExtensions form, please check out this page: Save and Continue in miniExtensions Form