I think this happened to me. I use the "New threads" button near the top. If that is what you use make sure that after you select it that ONLY "Show only: Unread x" shows as below across from the "filters" pulldown. Any other filters get stacked on it and will make showing anything else problematic. See pic below.
Was user error on my part. I use the “New Posts” tab to see what’s new. That in turn pulls up a pop up (iPad w/ Chrome browser) that has all the forums listed with check boxes for which ones to list. Some random action on my part part had them all unchecked. PEBKAP.