The Ubuntu supervisor package (3.3.1-1.1) has the configuration file in /etc/supervisor/supervisord.conf.
For some reason (I don't know why) there appears to be another configuration file in /etc/supervisord.conf and supervisorctl prefers that file.
You can either define the configuration file location explicitly to supervisorctl:
sudo supervisorctl -c /etc/supervisor/supervisord.conf reread
or just remove /etc/supervisord.conf.
