Hi –
If you place the cursor on to Sandwich Guildhall Museum 2019 and then scroll down you can see the entire submenu list and it won’t be cut off. Give that a try.
This is the intended behavior of the menu. It disappears once the page is scrolled beyond a certain point. It’s not something we can change with CSS. You’d need to redo the entire menu.
The easiest way to change this would be to create a “museums” page and link only that in the menu. Then, on that page, list each museum by town or area out. Folks could scroll through the page with out the menu getting cut off.