@djpaul I too tried following the same steps you outlined above (i.e. changing the slugs) and site wide forums are still not working for me. Its important for me to have the Component Box enabled as I need it enabled so the forum functions show up for the Achievements plugin. Any suggestions or detailed steps you can provide?
The trick for me was following her tip, “If you have any trouble, you may want to try unticking the Discussion Forum box in the Components setup page.” So my forums work now however because this box is unchecked I cannot use the Activities for the Achievements plugin. So if anyone has any help there it would be greatly appreciated.