Comment 4 for bug 1989302

Not very sure the reason. But the juju version in /var/lib/juju/agents/unit-juju-backup-all-2/charm/venv is newest version instead of 2.9.9.

And the stuck reason is because of the python-libjuju [0] is being deprecated. It's used in juju-backup-all snap when connect to controller [1] . Also the behavior is different in newest version.

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[0]: https://github.com/juju/python-libjuju/blob/master/juju/loop.py
[1]: https://git.launchpad.net/juju-backup-all/tree/jujubackupall/process.py#n27