Your browser does not seem to support JavaScript. As a result, your viewing experience will be diminished, and you may not be able to execute some actions.
Please download a browser that supports JavaScript, or enable it if it's disabled (i.e. NoScript).
In the Medusa sector chaos lieutenant mission, the Slaanesh altars do not show their area of effect as they circle for the coop player. He essentially had to just ignore them and get his shields and stances wiped every now and then.