Today was a new one. Checked in yesterday, upgraded overnight, checked app, said 2D, fine. Go through security, head to gate, arrive at gate 20 min before departure to see the red Xs, agent gone. I am a little concerned and ask the neighboring agents if I can still board this flight, as the agent seems to have closed boarding rather early. They are a little shocked that the agent closed the door 13 min early despite one passenger not having boarded yet. Somehow the system checked me out, so I didn't show on her computer as checked in, so she assumed I was a no show and closed up early. They raioded the plane, printed a boarding pass (lost my upgrade) and let me on fortunately. Guess I have to double check now after upgrades that I'm still checked in.