I have two sites I manage with Cornerstone and both hamburger menus are behaving erratically on mobile. The first is nemopro.com. It won’t work at all on mobile. None of the nav links work.
The second is http://www.springbranch.org. The bizarre thing here is that some links DO work while others do not. If you tap the ABOUT section, you can click the arrows on all four of the submenus and it will reveal the pages within them with no problem. However, none of the submenus work in the MINISTRIES or NEXT STEPS sections. Very strange.
Both sites have the latest versions of Cornerstone and X installed. I will send you login credentials in a separate private post. Thanks for your help with this.