One more followup to this. As recommended by the folks over at Formidable, switching over to the 2012 theme did solve the problem, and enabled the forms to be successfully submitted. Obviously, that is not the ideal solution, but helps to reveal that the issue is specific with the Ability template.
Right now the site is running on 2012 to enable users to make form submissions, but we would love to restore it to using Ability ASAP.
Thanks for your help,
Christian