Adobe Sign is not notifying AEM when document has been Signed, not returning completed Document of Record

We have an adaptive form that's triggering a pretty simple workflow, emailing the users on the form, collecting their signatures via Sign API, and then sending both parties a 'thank you' message with the completed/signed form, and CC'ing an email address for our agency.  The problem is that Adobe Sign does not seem to be notifying our AEM instance that the signing process is complete, nor is the completed Document of Record being returned to AEM.  This makes it so our last email workflow step never fires.  I can't figure out if this is an AEM or Sign issue.  Has anyone run into this?

Here's the gist of our Workflow steps:

1.) The form is submitted.

2.) Both users are sent a 'thank you for your submission' email via the 'Send Email' workflow step.

3.) User1 is sent a request to Sign via Adobe Sign api.

4.) User2 is sent a request to Sign after User1 has signed.

5.) The completed document of record is then sent via email to User1, User2, and CC'd to a third address. (this is the step that never seems to work)

If I look at the Workflow instance that's created upon submission, the process stalls at the 'Sign Document' step.  The initiator is listed as 'null', and no end time is specified (since it never completes).  

In the AEM config manager, I did check that the  Adobe Sign Configuration Service is setup, it looks like it's set to fire every 5 minutes (

*/5 * * * *).