Mobiel Menu Dissapearing

The theme is working perfectly for me and is a really great theme but one major problem I’m having is that when the theme is loaded on a mobile device, the menu disappears and the drop down list doesn’t appear.

I read that it seems to run into problems when the menu is quite large but I tested it with a smaller menu of only 3 items and it still doesn’t work.

I tried custom CSS as I read in another thread which was suggested
#access select{display:none;}

#access ul{display:block;}

This however just listed the first three menu items but the drop down list again didnt appear.

It seems like it’s not loading the JS which I guess is what turns it to a drop down?

Another small little thing I’ve forgotten how to do is the little box that appears at the bottom of a page to take you back to the top. I think I disabled this by mistake and I forget what the class name is to make it reappear.

The site I’m working on is https://www.cavendishhotel.co.uk/test/wordpress

If anyone can help I would greatly appreciate it

Thanks
Michael