With setting "Host Isolation response : Leave powered on", HA will only restart VMs in case a host crashes. In case it's only the management network which doesn't work, the host considers itself isolated and follows the above mentioned configuration. If you want the VM's to be restarted on other hosts in such a case (even if the VMs are still alive, but only the management network has issues), you need to set the isolation response to either Power Off or Shut Down.
André