The corresponding smoke test (mentioned in #1) passed for me on focal-ussuri:

2021-07-21 13:04:35 [INFO] test_901_pause_resume (zaza.openstack.charm_tests.ceilometer.tests.CeilometerTest)
2021-07-21 13:04:35 [INFO] Run pause and resume tests.
2021-07-21 13:04:35 [INFO]  ...
2021-07-21 13:05:05 [INFO] Testing pause and resume
2021-07-21 13:05:36 [INFO] ok

But 2 hours later my model was still up and I noticed the unit status changing spuriously to blocked, and back to active:

2021-07-21 14:53:06 DEBUG update-status active
2021-07-21 14:53:06 DEBUG update-status active
2021-07-21 14:53:06 INFO juju-log Unit is ready
2021-07-21 14:57:31 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 14:57:35 INFO juju-log Registered config file: /etc/ceilometer/ceilometer.conf
2021-07-21 14:57:35 INFO juju-log Registered config file: /etc/ceilometer/polling.yaml
2021-07-21 14:57:35 INFO juju-log Registered config file: /etc/memcached.conf
2021-07-21 14:57:37 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 14:57:42 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 14:57:46 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 14:57:51 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 14:57:55 DEBUG juju-log Generating template context for amqp
2021-07-21 14:57:57 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 14:57:59 DEBUG update-status active
2021-07-21 14:57:59 DEBUG update-status deactivating
2021-07-21 15:03:20 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 15:03:23 INFO juju-log Registered config file: /etc/ceilometer/ceilometer.conf
2021-07-21 15:03:24 INFO juju-log Registered config file: /etc/ceilometer/polling.yaml
2021-07-21 15:03:24 INFO juju-log Registered config file: /etc/memcached.conf
2021-07-21 15:03:25 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 15:03:30 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 15:03:35 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 15:03:39 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 15:03:44 DEBUG juju-log Generating template context for amqp
2021-07-21 15:03:46 WARNING juju-log Package openstack-release has no installation candidate.
2021-07-21 15:03:49 DEBUG update-status active
2021-07-21 15:03:49 DEBUG update-status active
2021-07-21 15:03:49 INFO juju-log Unit is ready

Looking at the service logs, it seems like the service keeps dying and restarting every 10 seconds:

Jul 21 15:17:38 juju-b5df3e-zaza-be83d51f921b-14 ceilometer-agent-compute[87733]: Deprecated: Option "logdir" from group "DEFAULT" is deprecated. Use option "log-dir" from group "DEFAULT".
Jul 21 15:17:43 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Stopping Ceilometer Agent Compute...
Jul 21 15:17:43 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: ceilometer-agent-compute.service: Succeeded.
Jul 21 15:17:43 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Stopped Ceilometer Agent Compute.
Jul 21 15:17:43 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Started Ceilometer Agent Compute.
Jul 21 15:17:48 juju-b5df3e-zaza-be83d51f921b-14 ceilometer-agent-compute[87769]: Deprecated: Option "logdir" from group "DEFAULT" is deprecated. Use option "log-dir" from group "DEFAULT".
Jul 21 15:17:53 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Stopping Ceilometer Agent Compute...
Jul 21 15:17:53 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: ceilometer-agent-compute.service: Succeeded.
Jul 21 15:17:53 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Stopped Ceilometer Agent Compute.
Jul 21 15:17:53 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Started Ceilometer Agent Compute.
Jul 21 15:17:59 juju-b5df3e-zaza-be83d51f921b-14 ceilometer-agent-compute[87817]: Deprecated: Option "logdir" from group "DEFAULT" is deprecated. Use option "log-dir" from group "DEFAULT".
Jul 21 15:18:03 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Stopping Ceilometer Agent Compute...
Jul 21 15:18:03 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: ceilometer-agent-compute.service: Succeeded.
Jul 21 15:18:03 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Stopped Ceilometer Agent Compute.
Jul 21 15:18:03 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Started Ceilometer Agent Compute.
Jul 21 15:18:08 juju-b5df3e-zaza-be83d51f921b-14 ceilometer-agent-compute[87862]: Deprecated: Option "logdir" from group "DEFAULT" is deprecated. Use option "log-dir" from group "DEFAULT".
Jul 21 15:18:12 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Stopping Ceilometer Agent Compute...
Jul 21 15:18:13 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: ceilometer-agent-compute.service: Succeeded.
Jul 21 15:18:13 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Stopped Ceilometer Agent Compute.
Jul 21 15:18:13 juju-b5df3e-zaza-be83d51f921b-14 systemd[1]: Started Ceilometer Agent Compute.

So most of the time, the update-status hook doesn't catch it and reports "active", but sometimes it does catch it and reports "blocked". Still investigating.