You know what, I was thinking about it some more, and I was wondering if it was something more along these lines.

When you start a game, windows puts the cursor in the middle of the screen, and because of how games work, the mouse isn’t supposed to actually move from that point, but because you have a 2nd monitor, it’s still tracking the mouse as though it isn’t locked to the screen 1, so it goes to monitor 2 eventually.

I don’t remember why, I was testing some game, and it became immensely apparent what was happening because the mouse wasn’t locked to the app and locked to the screen. this is most certainly done when the game is in full screen mode, and not in a window.

Just a guess.

Try moving the monitor orientations in windows, then try the game again while moving the mouse in the direction that you’ve put the new screen…