As you can see in the preview taken from the personalization page in settings, there should be a white border around the windows. The effect is that when I snap one to one half of the screen and another to the other side, there is a small gap in between where the white border should be. Like when you have a window selected, it will be highlighted by the border to indicate that window is front. This happened when I tried out 1903 months ago and is still present when I recently reupdated. This issue is not present in version 1803.
