While playing when I held down FN and pressed F# to adjust my volume or brightness and the game would flash to a black screen and be unresponsive for a second after that.
Thats likely the games window losing focus to display whatever UI your PC/laptop has for displaying volume. It might go away entirely if you go into options and stop the game running fullscreen. You can still run it the same size as your screen, but it changes the way the game behaves.