Comment 4 for bug 1695844

@Markus It seems libvirt doesn't have internal_access_path, so it won't run into this branch in which websocketproxy swallows the RFP message.
https://github.com/openstack/nova/blob/master/nova/console/websocketproxy.py#L147

But as Bob said maybe it's relative to the tempest problem which is to be fixed with this patchset: https://review.openstack.org/#/c/463259/

But it's also possible to be a different problem as there is a ResourceWarning complaining unclosed socket just as you posted in bug 1669468.

Anyway, it looks worthy to test by adding a sleep before this line,
https://github.com/openstack/tempest/blob/master/tempest/common/compute.py#L319
so that it will always contain the first RFP frame in the upgrade response. You can verify if that will trigger the error reported in 1669468.