Problem with mega menu

Hello, I have a problem with the mega-menu. Normally it looks like this (correct-megamenu.png), but when I edit something on the page (not in the header) and save the changes, then it breaks and looks without dropdown like this (incorrect-megamenu.png). All I have to do then is go in and re-enable the megamenu, but why does it work like this and how do I fix it?

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