This is caused by https://bugs.launchpad.net/juju/+bug/1897743 where the upgrade-charm hook is not run on 2.8.4 causing the venv to not be rebuilt to pick up any changed wheelhouse entries (in this case, a new dependency in the snap layer).
This is caused by https:/ /bugs.launchpad .net/juju/ +bug/1897743 where the upgrade-charm hook is not run on 2.8.4 causing the venv to not be rebuilt to pick up any changed wheelhouse entries (in this case, a new dependency in the snap layer).