I experienced this myself yesterday, but I think this could be connected to nVidia’s drivers 365.10, which I updated to yesterday. While I was on 364.72, I had no such issue.
To clarify on the issue, what I see when I press “Play” in simulate mode, the whole UI (of the editor, not the game!) resolution seems reduced (buttons look larger and so on), and indeed there is an offset in the position of the buttons (I had to aim the cursor between “Blueprints” and “Cinematics” for the “Stop” button to be highlighted). If I reduce the window size, the UI gets shrank horizontally and everything looks narrower! This is really weird.
@Davision, could you change this question into a “Bug Report” instead of “Using UE4” so that it gets the required attention?