this sounds like an issue with the 1099-R entries or supplemental questions after the 1099-R. You should go back through that section and make sure everything is answered. You can also try deleting and re-inputting the 1099-R again, especially if it was imported.
you can also check the IRA Information Worksheet in forms mode if you are on Destkop and look for anything missing or any errors. Double-clicking on Lines 6/7 on Form 8606 should show the related forms. For Online you may need to look at the PDF with 'all forms and worksheets'.
