Comment 18 for bug 1727355

This issue is not that Juju breaks when a new series is released. The problem is that Juju defaults to using the latest LTS as the series for which to bring up machines if none is specified by the user. If bionic becomes the latest LTS, Juju will try and find agent binaries to match. And if we are yet to publish those binaries in streams, we will get the error referenced in this bug.

So it's just a case of a small window where distro-info was updated but the streams publication lagged behind a little.