VMware vCenter collects data from ESXi servers with an agent. When this agent crashes, no performance data is available from the host and any VM that runs on the host.
First, to verify the existence of this problem, use the vCenter Client to observe whether performance data is available for VMs running on impacted hosts. To observe performance data, open vCenter Client and go:
Home -> Inventory -> Hosts and Clusters -> select a host that is missing performance data (Cloudamize might have sent an email with this information). -> Select the Performance tab -> go to advanced -> select a CPU performance metric-> select past Month.
You should see a message: "Performance data is currently not available for this entity" which confirms that the performance collection between this ESXi server and your vCenter is not working properly. Alternatively, some performance data might be available, but no recent data is available.
If performance data was not available, usually this problem can be fixed by restarting the VMware Management Agent. VMware provides information on how to do this.
Please find here 2 links that may help you resolve this issue:
Troubleshooting gaps in performance data or missing performance data in vCenter Server (1003878) (Step 1 is the mostly likely resolution.)
Step 1 gives the following link:
Note that this link is especially relevant when you are using HA (high availability) as it gives instructions to restart data collection agent without the HA taking any action. Specifically, see the instructions after "Caution: Ensure Automatic Startup/Shutdown of virtual machines is disabled before running this command or you risk rebooting the virtual machines."
When the management agent is successfully restarted, performance data should be available. You can perform the troubleshooting steps above to confirm that performance data is now available.
Note that a crashed management agent might not impact the performance of the VMs. However, VMs running on these host will be excluded in Cloudamize assessments. Once the agent is restarted, please check if the impacted VMs have been excluded from the assessment by going to the settings page in the Cloudamize application and enabling the impacted VMs.