Hi @Zyann ,
Heartbeat lost means ambari-agent is not connected to ambari-server.
can you see the status of ambari-agent on the problamatic host using the command :
[root@aanaik1 ~]# ambari-agent status
Found ambari-agent PID: 3516
ambari-agent running.
If its not running you can start it.if its running, please see in
[root@aanaik1 ~]# tail -f /var/log/ambari-agent/ambari-agent.log
whether its able to send heartbeat to ambari-server or not.
Hope this helps you