>20-30 minutes ago it was showing several messages for today. Now, clicking on that folder only shows one or two messages, at the most. It only shows the most recent message for the Chatter Forum, and is not showing any other forums at all (and, like I said, it was working just 20-30 minutes ago).

Yes, all that is normal. That option retrieves new messages. If you wish to obtain full messages for today, click on Today's button and so on for Yesterday's button, etc.