After restarting the nova-compute service when a guest with SR-IOV-based network interface(s) attached is running and removing the guest, it is no longer possible to attach SR-IOV VFs on that node to any guest. This is because available devices are enumerated on service startup but as the device is attached to a guest it is not included in the list of host devices. You must restart the 'nova-compute' service after removing the guest. After removing the guest and restarting the service, the list of available SR-IOV devices will be correct.