When I did the alt tab task, all I saw was a green screen.
From your "green screen" click the "Weather" app.
With that open, you should be able to grab it by the top "title bar", and drag it to the bottom of your screen. Hold it there briefly and you will notice it flip. At that point simply release your left mouse button.
Check taskmanager, it should disappear in 10 or 15 seconds.
IF you use another method to close the app, like clicking the "X" or just dragging it off the bottom of your screen without allowing time for it to flip, then it will remain in taskmanager as you're experiencing