sometime vorpx can fail to hook up on your dk2,
you might want to try the trick with oculus demo scene,
1. First, run oculus config demo scene keep it open
2. Then run your game as usual
3. After inside the game, press alt tab and close demo scene and oculus config
4. Check again inside your oculus, and see if vorpx is hook up on dk2 now,
sometime this little trick work fine
but sometime game made with UE4 tend to produce crash or freeze after the logo, anyone have similar issue ?