If the game window disappears, or fails to show up, when launching the game or transitioning from the launch menu into the game, you can try enabling a new feature from within the config.ini file located within the config folder of the game’s install directory. Add the line:
Multithreaded = False
To the bottom of the config.ini file to force the game into single-threaded mode. This seems to fix the window not showing up. An option will be added in-game to toggle this, but for the time being modifying the config.ini works just as well.