So since no one from Microsoft has pitched in here... Here is the issue as I've noticed. Certain games run in a controlled "full screen" mode... So when another app tries to take front and center, the full screen game closes. That is why this doesn't happen for browsers and such.
The issue is the Windows 10 Action Center toasts.
To prove my point, setup some form of action center toast, for example, if you have an android phone you can have it connected to Windows 10, and it will notify you when your battery is going low. Play a fullscreen game and wait for that toast to happen, once it happens the game minimizes.
The issue is the same issue since the dawn of Windows "balloon" notifications. The balloon used to attempt to take front-and-center and it would minimize your game, normally during important points in your game. Now it isn't the balloon, but the toast notifications.
So you can either disable it completely or complain enough to MS and ask them to let the toast happen in the background.
It's rather frustrating!
One way to fix this is to right click and turn on "quiet hours" while you are playing the game.