Other functions within Deployment Manager appear to be working. Why would the job step notification be failing?
A runtime shutdown hook forced a halt and ended several services (seen in the server.log) including [org.jboss.jms.server.destination.QueueService] Queue[/queue/SPSSNotification] stopped. Attempts at opening job step notifications would produce the log message:
Completely shutting down C&DS and restarting C&DS resolved the issue.