Ninja dear pankaj, this issue isn't depends on template or plugin, it's bug of recent T4 versions, 'cos prior versions of T4 had no such bug and worked well. I started this thread as T4 bug, and saovry see the same bug with recent T4 (and yes, he use simple T4 Blank) His picture isn't illustrate it good, better to illustrate it with video
I wrote about your Stark online demo just to illustrate that it's working on your site just because your demo use old T4. If you check the same demo on recent T4 versions (1.1.3, 1.1.4) - it will have a problem.
(1. click on any 1st level menu to open list of 2nd level submenus 2.try to click it again to hide 2nd level submenus 3. nothing works.)
and thank you dear saguaros for compare page, later I'll try to figure which changes in T4 caused such bug with mega menu collapsing in mobile view.
I hope, alltogether we will solve this problem to make T4 more perfect again