Thanks for the reply, @GangWar. 

The issue is sorted out now. As you said, the issue got fixed after checking the config.ini. The  inter communications between the client and server were made to do over TLS, but we disabled the TLS/SSL in UI and for all agents. This was the main cause, as the heartbeat tried to get a response, but it didnt. Changing the configuration in Cloudera Manager -> Administration -> “Use TLS Encryption for Agents” should be unchecked, and restarting the Cloudera Manager fixed the issue.