Nestable fields don’t appear to be working with the Mailchimp action panel. If I add a field using the regular method the fields are listed in the drop downs but not the nestable fields. You may have already addressed in the upcoming version but thought I would mention it just in case.
The select fields have caused problems in different situations – therefore, with the new version, those select fields have been replace with basic input fields. You can just insert the data you want there