do others see you online?
if so, then it's the application on your phone. Or the connection between their app and their server.
It works kinda like this. You enter details for an account. It's then "connected" on their servers. Their server knows whether your phone is connected to their server. If it is, it passes the info to your phone as things change (x logged in, y logged out, z sent you a message). If your phone isn't connected it either emails (if you set it up) new messages, or sends them via push to your phone. When your phone connects again to their server it has a queue waiting and pushes all that information to the Beejive application.
Basically. If others see you online, but you aren't seeing them, it's likely a bug on their end. Either on their server software, or on the application.