CIS is installed and configured. For more information, see Planning Your Cloud Integrated Storage Server Environment in the OES 2018 SP3: CIS Administration Guide.
Port 8000 must be opened on all OES servers where core and dashboard agents are running. So the agents can communicate with the CIS server.
Ensure that the coreagent and dashboardagent services are running.
For more details of OES Health tab, see OES Health in the OES 2018 SP3: CIS Administration Guide.