Scenario:
vSphere all versions
Since the vSphere HA will only take action when there is an unexpected power off of the virtual machines, a graceful shutdown of the VMs for a hardware maintenance will not failover the VMs to other hosts of the cluster.
Same can occur depending on non-default adjustments in the vSphere HA or lack of resources in the cluster to power on the VMs.
Manually register the virtual machines to other hosts of the cluster following these steps: