Sub-menu on mobile responds with hover effect

Hello all,

on my customer’s site the sub-menu mobile reacts very strange.
When you tap on sub-menu items, they jump.
If you set the window very narrow in the desktop browser and so have the mobile view, you can see that JavaScript reacts when you mouse over the sub-menu.
So I suspect that there is a hover function that actually works for desktop views also in mobile.

That’s the page:

The sub-menu is “Vermietung”.

Hope you can help me, maybe I can’t see the problem.