Verify there are no other test, failed, or abandoned field map layouts created for the same form, if there are delete them. Also, verify the “Signature” option is selected on the format dropdown of the field map for the signature field.
If the above is confirmed, then complete this form if we can login to the installation to determine the issue, or if not possible, use the same form to upload screenshots of the plugin’s “Export” tab with the field map layout selected and the “Settings” tab, and the “Under the Hood” tab for further review.
We remain at your service.