It all started today, it had not happened to me before. Whenever I launch a game which is set to work fullscreen from startup, the game loads a couple frames in my primary monitor before freezing on it and switching the graphics/display to the second monitor.
If I start the game on the second monitor, the same happens.
The thing is that the game only detects input in the first monitor, as if the game was displaying on it.
I'm using Windows 10 Home, latest update if I had to guess because it always updates automatically.
Ask me anything if you want to know anything else!