ArcGIS Monitor checks the health of your ArcGIS Server by accessing the server's Health Check API every 15 minutes.
Health Check—ArcGIS REST API: Services Directory | ArcGIS for Developers
The health check reports whether the responding machine in the ArcGIS Server site is able to receive and process requests. A healthy (available) site will return an HTTP 200 response code along with a message indicating "success": true. An unhealthy (unavailable) site will return messaging other than HTTP 200.
You can manually perform the health check by entering the HTTPS commands below in a web browser - substituting your fully qualified GIS Server name or web adaptor host name.
ArcGIS Server Health Check
- https://webadaptorhost.domain.com/webadaptorname/rest/info/healthcheck?f=json
- https:/gisserver.domain.com:6443/arcgis/rest/info/healthcheck?f=json
- http:/gisserver.domain.com:6080/arcgis/rest/info/healthcheck?f=json
In your situation, the Health Check API test being executed by ArcGIS Monitor (as part of the ArcGIS counter) is failing. Check your ArcGIS Server log file for errors. Normally a failed Health Check would mean your ArcGIS Server is unavailable (crashed, unresponsive, etc.) but I would think you would notice that - so I am guessing you are still able access your ArcGIS Server service and successfully login to ArcGIS Server Manager.
Try to use the HTTPS syntax above to manually execute the Health Check from your web browser running on the ArcGIS Monitor server and from your laptop. The expected response should be:
{"success":true}
If you don't get this response, contact Esri Support to troubleshoot this ArcGIS Server issue.
If you the HTTPS command works from a web browser on your laptop but fails when run from a web browser on the ArcGIS Monitor server, check with your network administrator to verify any connectivity/firewall issues between the ArcGIS Monitor server and the GIS Server.
Please verify you did not make a typo when you entered the ArcGIS Server site under the ArcGIS counter.