How can I fix my Main menu disappearance on sim gallery pages?

When I browse Any SimGallery pages (Latest Photos, user dashboard,...), my main menu disappears (not visible on the page, but it's there when you inspect the code) and some div elements blocs moves to the next line. But everything is fine on all the others pages. I assume it's a jquery conflict but I was not able to locate the problem. Thanks for your help.

A simgallery Page on my website : http://authentikultu[...]37/vos-partages

See the page on the image attached