Got a weird one. The container width is set to 1300. I add a Header Element with a Smart Slider 3. When I added sticky navigation I notice that the Header was about 1 px wider than the navigation on the left side. So I checked to make sure everything was set to 1300 including the slider although it is set to auto.
On a lark I changed the container width. Even widths have that extra pixel and odd widths have line up.
So 1300 or 1302 => extra pixel and 1295 or 1301 => line up.