Bug with the hamburger menu

I’m building a website in generate press but I’ve run into an issue with the hamburger menu on iPads (portrait mode). It looks great in the preview (on desktop), but when I look at a real iPad it doesn’t switch to hamburger menu, it is simply a very buggy looking desktop menu.

On iPad: https://i.imgur.com/PUnVTsL.png
On desktop (wordpress preview: tablet): https://i.imgur.com/xVBl1OR.png

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