>Yesterday I got an email from Facebook saying that I had 4 messages waiting for me. I opened the app, it showed a little balloon with "4" in it. I clicked it, and there were no messages

I also get this, but now it's always stuck at some arbitrarily high number. in the past few years I've reduced my fb usage to a couple of minutes per month, down from a few minutes per day. I'm sure it's underhand tactics like these (tricking a billion dormant users) which upholds their claim of 2 billion "active" users or whatever bullshit number it is