Third level menu items don't appear on mobile

Hello, I still really love your theme. I created a CHILD theme right now for it because I need to solve a problem. But… maybe you already tackled it. So here I am to ask for support.

In the mobile version (we are testing it by different versions of Android) the third level of the MENU is not visibie.
So: you can see the first level and the second level, but if you click to see the third level, what you can see on the computer is not visibile on the mobile version.
Can you take a look on this site using a smartphone and tell me if there is something we can do to fix it? The child theme was create right to solve this problem and to try to modify the theme for another issue (related to header image + search box).

Here you are the website: https://justb.it

If you tap on “chi siamo” (first level) and after that you tap on “insegnanti e collaboratori” (second level) the third level doesn’t appear. If you do the same from a computer, everything is ok.

The problem is active on your original theme and I created a child theme to try to fix it. Hope you already fixed it in some way…

All the best,
Marco