1) Take a back up of discovery_agent folder and delete the discovery_agent from the hub with problem(s)
2) deploy the java_jre again to the hub with the problem discovery_agent(s)
3) run a delete query from the back end database to remove the discovery _agents from the CM_DISCOVERY_AGENT table
delete from CM_DISCOVERY_AGENT where hub = '<Hubname>'
4) deploy the discovery_agent back to the problem hub(s)
5) deactivate and activate the discovery_server
6) wait 10 minutes