Just logged https://github.com/chef/chef/issues/3835
Looks as though the systemd provider/helper is broken - an internal method
used to determine of the unit file is available returns false during the
platform supports lookup; the false return is not handled.
It would seem this is never likely to succeed on my infrastructure, with
many thousands of systemd units, we have to be super careful to not iterate
through them; dbus hangs, etc.