Menu Sub Items not showing on mobile

Hi,

I am rebuilding a website using the twenty seventeen theme. All is well on desktop and tablet, but when viewing the site on my phone, I cannot access the drop down sections of my top menu. There are no arrows and sub menu items are not available.

I have disabled every plug-in and the problem persists.

Does this issue sound familiar? Can anyone please help?

Thanks,
Andrea

The page I need help with: [log in to see the link]