I admire your patience.
In the previous state the situation was:
Oddly http://klantwebsite4.nl/has a nav menu with a padding above te nav (the slider_sectie), while http://klantwebsite4.nl/behandeltechnieken/ looks good (page header from GP) but when i shrink the window to tablet width (hamburgermenu) the nav ducks lower.
But now it’s exactly the reverse state. In desktop view on the pages with the page header there is a margin at the top, and in the homepage with the slider it’s exact in the right place. In hamburger menu (under 768 px) the pages look good, except the slider.
Hope it doesn’t give you a headache…