Comment 1 for bug 1755155

If you have very large configuration, I think upgrading the agents in the model might fix some of the things like "unexpected end of JSON input".

IIRC, the issue is that in 2.3 (2.2?) we introduced a json/websocket library that can transmit responses in frames, that ended up not supported by older clients.

And looking at the status output, it does look like all the agents in the "openstack" model are running 2.1.2 still, while the controller is running 2.3.4.

That should be as simple as:
 juju upgrade-juju -m openstack

(if necessary, you might pass --agent-version=2.3.4)