for anyone interested, here was the resolution to this ticket:

For that call, the Single-Step Conference (SSC) was attempted before
the Network Reached and Established Events were received. For
outbound calls, to ensure a call is in the proper state, please have
the application wait until the Network Reached and/or Established
events are received prior to sending the SSC request.

Thanks for posting the resolution! After speaking with the engineer who handled the ticket, the SSC was being sent before the first response from Communication Manager/AE Services indicating that the call had reached a stable state. Those would be indications such as Network Reached, Delivered, or Established.