OnCommand Unified Manager data source object failing to refresh with error "Unable to invoke AU EJB"

Applies to

OnCommand Unified Manager 9.5 Linux 

Issue

After adding back a cluster it fails to show connected and start polling. 

Note: The below error can be seen in the ocumerror.log.

ERROR [oncommand] [pool-23-thread-18] [c.n.i.c.u.AcquisitionUnitStatusUtil] Unable to invoke AU EJB 

Note: The below error can be seen in the ocumserver.log.

ERROR [oncommand] [pool-23-thread-5] [c.n.i.c.u.AcquisitionUnitStatusUtil] Unable to invoke AU EJB
java.io.IOException: Failed to retrieve RMIServer stub: javax.naming.ServiceUnavailableException [Root exception is java.rmi.ConnectException: Connection refused to host: localhost; nested exception is:
java.net.ConnectException: Connection refused (Connection refused)]
at java.management.rmi/javax.management.remote.rmi.RMIConnector.connect(RMIConnector.java:370)