Symptoms

Seeing "Root element is missing" errors when hitting a point in the workflow. The event where it errors on, is a smartobject event that is executing a WCF service.
 

Diagnoses

After looking in the SmartObject Service tester tool, we have noticed that the smartobjects were there, but the service objects for the WFC service was missing.
 

Resolution

After we manually created the service objects on the target server, we were getting timeouts on one of the instances that communicates with and Oracle DB.

To fix the issue, we removed the Service Instances that we manually created, and then retried deployment with K2 PandD to import the missing ones. After doing that, the issue was fixed.