Problem: Dropdown Menu on touch devices (in twentyeleven childtheme)

Hey guys,

i’m having a Problem with the Menu in my Twentyeleven childtheme.
In the Original twentyeleven-Theme it is possible to use the Dropdown Menus on an iPad or other touch device without Problems and to any depths.
In my Child theme (in which i didnt change anything about the menu except the ‘#access’ css) the submenus often disappear suddenly and it is not possible to get to pages with a depths deeper than in the first submenu.

This is the Site that i am talking about: https://www.gjh.de/frog/

I hope here is somebody with an ipad who can help me.

Thank you and greetings from Frankfurt,
Jonas