So this seems to happen when a new input is detected, like a Bluetooth controller, or if your controller disconnects and you reconnect it. If you click on the sign-in when it pops up, you will be signed in twice on the same account. This is what breaks the game, and will ruin any campaign you are in, load, or start. Just closing the prompt will not ruin your game, and you can keep playing with a controller. This will happen if you are already double signed in when you start the game, as well. To check if you are double signed in, start a new campaign. When the loading bar pops up it should say CAMPAIGN 1(1). If it says CAMPAIGN 2(2), your campaign is fucked. If it doesn't even let you start a new campaign, like in the video, then you're probably double signed in. Also, this is what causes the flashing/strobing lights in campaigns, the floating camera/disappearing chief bug on load ins, and if you do this in game you may well enter an infinite death loop. So DONT SIGN IN AGAIN OR PRESS LET'S GO.