How reproduce

• go to the demo: https://demo.ametys.org/nightly-intranet-cms/preview/intranet/fr/boite-a-outils/contribution-sur-l-intranet.html
• at the bottom of the page insert a link to a cms page
• go to the preview
• click on the link
• return with the arrow of the browser to the other page

The menu bar does not attach below the menu