Comment 7 for bug 1875481

As an aside, one issue Juju currently has is that if the leader unit does away, there is not an immediate election of a new leader - the leadership lease needs to time out. This can take up to a minute. So that could explain the symptom. See bug 1469731

It comes down to: was there > 1 unit asked for, and why was unit 0 removed. If possible, until bug 1469731 is fixed, it's best to try and avoid removing the leader unit.