This happens when the cluster's agencies are disabled in EAM. This usually follows the use of the VSAN Shutdown Wizard, where the Restart Cluster Wizard is not used to restart the cluster afterward, which re-enables the EAM agencies as part of the workflow.
Resolution
This must be resolved with the workaround below. For future operations, please make sure that the Restart Cluster Wizard is used after the VSAN Shutdown Wizard.
Workaround: Before starting, ensure the VMs on the vsan cluster are running without accessibility issues
To re-enable the EAM agencies on the cluster:
Obtain the clusters MOID by selecting it in the vSphere Client and using the address bar to find the domain-c#### identifier.
From a browser, access the EAM managed object browser (MOB)
https://<VCENTER_IP>/eam/mob?vmodl=1
Click on Enable and it will open a pop-up window.
In the value field "<cluster type="ClusterComputeResource" serverGuid="Server GUID">MOID</cluster>" replace MOID with the domain-c#### value you collected in step 1.
Click Invoke Method.
Give the cluster a few minutes after the enablement to deploy the vCLS VMs.