Comment 2 for bug 1921336

This looks like the result of having the leadership pinned during the upgrade-series preparations step, then the pinned unit removed.

This would mean that the completion step did not cause the leadership to be unpinned from the removed unit (no longer associated with the machine), so leadership remains locked to an absent unit.

A work-around if the cloud can withstand the churn is to:
- Stop the controller machine agents.
- Delete the contents of /var/lib/juju/raft on each controller.
- Restart the agents.

This will cause Raft to re-elect new leaders for all applications, but it will evict the frozen leader.