Comment 9 for bug 1551150

Do you know if the phone actually uses systemd as its init system nowadays?

LXC requires either systemd or cgroup-lite to mount all the cgroup bits properly, if systemd is installed but not used, that could explain what you are seeing. Installing cgroup-lite should have fixed it though, unless the container is started before cgroup-lite is done. That's not possible with the regular lxc init script, but if the phone has something custom, it could be possible.