Suddenly not working on mobile

Hi, I installed and configured Sydney theme which I like very much, but now I tested in mobile (with two different mobile phones and different browsers) and it does not work.
Just open the home page and click the nav menu ABOUT US (which is the only page active for now) and the mobile menu appears completly destroyed and the page is not responsive at all.

Never happened before, please help me!

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


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