Add cart button to nav bar/Checkout button not appearing

Okay so this is weird!

In ‘Design Mode’ the option to ‘view cart’ is quite obvious; however….

When published, it’s not visible on the mobile device, neither on mine, or clients phone, and I somehow I managed to remove the cart button as well. So there are two things I need help with:

  1. How do I add the cart button to the header for checkout?

  2. How do I make checkout visible on the mobile breakpoint, from the ‘view cart’ drop down?