CAU was working for some time (I was really surprised that it did actually work without any hitch, being it MS product...)
But it is back to its old tricks:
Failed to put node VHOST01 in node maintenance mode. Details: Microsoft.ClusterAwareUpdating.ClusterUpdateException: Could not suspend cluster node "VHOST01".
at MS.Internal.ClusterAwareUpdating.Util.CheckPshError(PowerShell shell, MulticulturalString exceptionMessage)
at MS.Internal.ClusterAwareUpdating.FailoverClusterImpl.PutIntoMaintenanceMode(String nodeName, ICauPluginCallbackBase callback, CancellationToken cancelToken, Boolean force)
After which it seems that it just rebooted the host with all VMs crashing & restarting on the other host in the cluster and the update finishing on both hosts with Success (I would call it otherwise)
Nice, really nice...
Anybody has any idea what that "warning" means