I have the same problem on several X-theme powered websites. In all of them the submenu doesn't work on mobile.
x-body.min.js:1 Uncaught TypeError: window.csGlobal.collapse is not a function
at HTMLDocument.<anonymous> (x-body.min.js:1)
at i (jquery.js:2)
at Object.fireWith [as resolveWith] (jquery.js:2)
at Function.ready (jquery.js:2)
at HTMLDocument.K (jquery.js:2)