Responsive enu disappearing on Desktop and Mobile

I've exactly the same problem on your demo site and here

igermoglidelsicomoro.it/sito/

If I visit your demo or my site with the stock samsung SGS4 browser, the menu appear and disappear after a second.

If I visit using Chrome everything works.

What can I do?

galaxy devices have bug in their default browsers. Since this is rely bug that is against all standards and if you want to care about galaxy devices I can only offer you to convert that menu to bootstrap menu but as custom payed job.