In short, for some reason when the page is shrunk down (mobile size) the menu goes to a hamburger menu but overlays the first element on the page. I don’t understand why the mobile menu does not push everything down the page so to speak. I assume there is something simple here I’m missing but this seems like a bug.
you have a Header Element that is set to Merge with Site Header. Which is causing the issue.
Not sure you need that option but you can set it to Desktop only.