Only with this information it will be hard to tell what is the issue.
Does your index page’s layout is set to column? Because I noticed that when you open the menu, it pushes the Session page down.
Can you share your editor? Only with the ability to see (not to edit). Do you know how?
Settings → Genral → Change the dropdown to “Everyone can view”
Then share the URL of your editor here.
On the index page your header is inside a group - whereas it’s not on the other page…
I just increased the z-index in dev tools of the header on the index page it it worked as expected… so try bringing the header to the front (or just remove it from the parent group)… either of those should work.