The messenger system built in to the world's most used social network, Facebook, has a couple of "hidden" inboxes. You may have messages that you've never seen - believe it or not. Hidden relatively deep within your Messenger inbox system, you'll find two boxes, one marked "Requests", the other marked "Filtered". There's also a THIRD sort-of-secret inbox, depending on how you've used Facebook Messenger in the past, one called "Archived." You'll want to see the whole lot if you've noticed friends disappearing over the past several years.