Comment 5 for bug 1928238

$ juju upgrade-series 78 complete
machine-78 complete phase started
machine-78 started unit agents after series upgrade
ntp/124 post-series-upgrade hook running
ntp/124 post-series-upgrade completed
ceph-osd/18 post-series-upgrade hook running
ceph-osd/18 post-series-upgrade completed
filebeat/853 post-series-upgrade hook running
filebeat/853 post-series-upgrade completed
nova-compute-kvm/16 post-series-upgrade hook running
nova-compute-kvm/16 post-series-upgrade completed
hw-health/7 post-series-upgrade hook running
hw-health/7 post-series-upgrade completed
telegraf/859 post-series-upgrade hook running
telegraf/859 post-series-upgrade completed
ceilometer-agent/61 post-series-upgrade hook running
ceilometer-agent/61 post-series-upgrade completed
neutron-openvswitch/59 post-series-upgrade hook running

As you can see, n-ovs post-series-upgrade runs after nova-compute-kvm finishes. This is likely a juju bug that should potentially perform post-series-upgrade hooks for subordinates before principal charms.