Issue menu on iPhone and Android (vertical view)

Issue menu on iPhone and Android (vertical view) I my users (including me)  experience on various mobile phone an issue with the "sub" menu of the theme. I made a youtube movie to show it.  (https://youtu.be/vic57YBBoLk) When you use your phone vertical, you can tab the menu, that is working fine. But when you want to click the little arrow for a submenu it doesn't work at all. This happens only in vertical mode. When you use your phone horizontal, it works fine.