I am also having mobile menu with sub menu issues using Safari and Iphone 6. The site looks great but when there is a sub menu, menu button only shows sub menu and not able to open menu page. Pressing the button just opens and closes the sub menu link. I've found that if I double tap and choose "open a new window" it can open but that is not something functional for the general public. It would make sense to me that pressing the menu should drop down both the main menu and sub menu pages to choose from. My website http://newportfertility.com/blog/
Ok, I figured this out on my own and the WP support site. I will post so others can learn as well. The sub pages are not created under a clickable page but just a link. use the "#" character in the URL field and name the link whatever you want. Then add this to the menu and you can position it by dragging and add sub pages to this. Now when it is clicked on the top it will not go anywhere and only show the sub pages. See below Rather then using empty pages, use the custom links box, and use # in the URL field, it'll be clickable, but not go anywhere, and you can give the item any name you like.. (without a need to create a page). If you don't see a "Custom Links" box, click on "Screen Options" (top right), and check the appropriate checkbox to enable custom links..
