Settings screen when I boot up the game shows me at Full Screen, 1920 x 1080 (the 1080 is my *desired* resolution rather than the screen's actual resolution, and is what I use in AnyRes). Actual resolution of the screen is 3840x2160, if it helps.
Also, FWIW, I'm not launching the program with any command line arguments (I know that can sometimes do weird resolution things)