CentOS - Oct 2017 - serial guests not booting until console attached

Since the update to 7.4.1708, I've got one KVM host that behaves very 
similarly to:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=686524

These guests were installed with (snipped for brevity):

virt-install --name xxx --memory 2048 --vcpus 2 --location xxx --disk 
xxx --disk xxx --network bridge=br0 --graphics none --autostart 
--extra-args "console=ttyS0 ks=xxx" --rng /dev/urandom

Those guests simply hang until I use "virsh console <guest>", at
which
time I see kernel messages immediately, so it seems like the guest's 
GRUB2 runs normally, but the guest kernel does not.

Is anyone seeing similar problems?