collaps mobile menu

Hello,

I found a solution in this support firom, but there is a little problem to work fine with my case.
Here is the answer I found:
https://kriesi.at/support/topic/submenu-items-in-mobile-menu-collapsed/#post-739288

But my problem is that the + icon doesn’t display for second submenu with avia mega menu.

I explain. Here is my menu

First level : + (displays fine)
– second level mega menu : no +
— cannot see this item
— cannot see this item
— cannot see this item
— cannot see this item
— cannot see this item
– second level mega menu : no +
— cannot see this item
— cannot see this item
— cannot see this item
First level + (display fine)
First level + (display fine)
First level + (display fine)

So I can open first level menu item that is no mega menu, but I can’t open Second level menu items that are mega menu item because there is no +icon.

Could you help me to fix that ?

Thanks
Carosch