Is the monitoring functionality independent off the cluster it is monitoring being up to see monitoring?

Control centre eats its own dog food. All its data is on topics. That means if your cluster is unhealthy you can see healthy stats until the control centre consumers have caught up. Which means if you have a lot of data and load, control centre can start lagging and in one case I had some very hard debugging wondering why control centre saying the cluster was unhealthy but the cluster was up. It turned out control centre was lagging by 24 hrs so I was seeing the previous days outage.

Confluent recommended putting control centre on its own cluster for this very reason. One that isn’t cheap, a minimal prod cluster is 3 brokers+zookeepers and secondly what then monitors your monitoring cluster.