Sub menu does not appear in mobile dropdown (off-canvas works fine!)

Hi,
on my site i can't open the submenu of the first menu item in mobile view - clicking on the "open arrow" has no effect.
Any ideas??
demo.meine-agentur.com/
Same menu with off-canvas is working: demo.meine-agentur.com/leistungsportfolio
Kind regards
Dirk

Hi Dirk.
Thank you for using our product,
Please give me link your site and your account of administrator via email: This email address is being protected from spambots. You need JavaScript enabled to view it.
I will fix it for you soon,