Also, you need to give the roster a little time to fill. When you get connected, your comp cant see everyone thats online immediatly. Depending on your system specs and connect, it might take a few seconds to register.
Same and even more noticable in the Main Arena. If theres up to 500 people online, i usually give the game a min or two to settle down (untill then, youll see the dar bars on the map change quickly and randomly.).