Please do not misunderstand. I do not want to criticize, but help to improve the plugin.
1)
Missing END Tags
Answer to your reply: then the problem is in another place. Please see with Firefox your own demo: view-source:https://demo.accesspressthemes.com/wordpress-plugins/ap-mega-menu/horizontal-mega-menu-demo/
You can see in red tags that have a problem. I think there are missing div end tags…
2)
When I open the mega menu on a small display and then – with open menu – I resize the window to large, then I resize again to small, then the toggle icon change the status, is wrong.
You can test it on your on demo on: https://demo.accesspressthemes.com/wordpress-plugins/ap-mega-menu/horizontal-mega-menu-demo/
1) Small display (<breakpoint):
2) Open Menu item Mega Menu
3) Resize to large (> breakpoint)
4) Resize to small
5) Click on close/open menu icon
6) Now you can see that there is a problem.
7) I solved the problem with this hack:
a. Insert in front.js circa on line400 this:
b. $(this).parent().find(‘.wpmm-mega-wrapper’).hide();
3)
When I change the breakpoint in your plugin (AP Mega MENU > Theme Setting > Theme > Responsive & Mobile Settings > Toggle Bar Main Setting > Responsive Breakpoint) then I have a problem with the breakpoints that are static in the file responsive.css
In my case I resolved hacking the responsive.css