Cover block not stabil

I want a stable cover with a full-width image, a heading page title and the (Max Mega) menu in the right place. Stable on my mobile and on a normal computer. trends setter.nl/wellnesshotel-design/

Sometimes it works, but later the proportions can suddenly change. Really don’t know how that happened.

Structure:
<group, fullwidth> <group, logo etc> no problems here

Again the <group, full width> and then <cover, with image, 1371x353px, alignment none, content position top/center>
then in the cover: <stack, justification center> then under stack <heading, h1><spacer><shortcode, Max Mega Menu>

The problem is that the image doesn’t stay on the full width and then strangely decorates the height. And so the h1 and menu. Things are not stable.

How do I solve this.

The page I need help with: [log in to see the link]