Can you please check this?
https://bugzilla.redhat.com/1666795
It seems that under certain unclear circumstances, during 4.2 -> 4.3 host
upgrade, the file ownership and permissions of VMs disks got set as
root:root and 640 instead of vdsm:kvm and 660 and so vdsm fails to start
the engine VM.
Manually fixing it seems enough to bring the engine again.
Can you please check and report? if it's that, it definitively deserves
more attention since we already got more than one evidence.
I also had this issue with a VM that was running during the upgrade from 4.2.8 ->
4.3.0. The situation was exactly as described in comment 26 of