I used an installer created from the develop branch in early December 2017.
So I can definitely say that when the constructor gets called again it's like a whole new instance of my game has started. All of the values are null / 0. Even the GraphicsDevice is null, but upon creating it I get a crash that mentions that the GraphicsDevice has already been started on the system.
Yes, unfortunately there's nothing here that's useful... I can't go to any code before the constructor. The stack trace literally looks like when you first start a game and hit the Game1() constructor.
My suspicion is that there's an Active event that MonoGame is hooked into to start the game... but that same event seems to be fired again when the game resumes from suspension which is causing this to happen. I have no evidence of this, but I can definitely say this isn't coming from my code.
All UWP games default as a Single User Application, but you have the option to opt in as a Multiple User Application. If you're making a multiplayer game you'll have to do this, because it's the only way to have more than one Xbox profile interact with your game. When you swap over to Multiple User Application the game behaves differently, and you get several more Xbox Requirements you have to meet for certification because of this. I had originally opted in as a Multiple User Application because I wanted the ability to Switch Users from the main menu, but I can totally get by as a Single User Application and plan to do that so I can get around this test case.