We just disabled all plugins and see that this problem comes from Revolution Slider plugin. Please update it to the latest version that you can find in basel/inc/plugins folder.
Yes you where right .. REVSLIDER was fiving a lot of problems ..
Now I removed revslider and the mobile menu is workinf again .
Now I have a question .. How can i importa a slide that is exactly the same of the demo site ??
I have installed the dummy data , but the homepage slide is not there .
You can find all the sliders import files in basel/inc/dummy-content/ folder and try to import them manually via admin panel -> Slider Revolution -> Import slider.