For the past month or so, I have experienced that the game is opening on my secondary monitor as a default. How do I change this back to my primary monitor?

I have already tried to change the settings in game. But it doesn't do any good. The first time it opens on the monitor chosen in-game, but ...

https://gyazo.com/0a0e05918baacbebd89a37fc0c949e21

I have found that the biters don't really know what they are doing when stepping upon a transporter belt.. So for the time being, this is my best defense against a melee biter attack. For spitters you could add a belt in a circle around the turret ...