[CentOS-virt] VM fails to start on host bootup, but starts fine manually. Why?

I have 5 VMs on my host.

The first four are setup to start on boot. But only the first three end up running. The fourth has to be started manually.

"Start virtual machine on host bootup" is checked on all four VMs but the fourth VM does not get started on host bootup. After the host boots up, the VM is "Shutdown" state. If I go into "virt-manager" and click "Run", it starts just fine.

I looked in /var/log/xen/ and did not see anything related, but I don't know what I'm looking for.

Any suggestions?

Best, -at