mega menu on sidebar does not work properly anymore

Hello,

since i have updatet the theme and the child theme to the latest version, the mega menu on the sidebar does not work anymore properly, the menu works but the slide out sub-menus can’t be seen.
Before with the old theme and child it was ok. I am using the price comparision theme and the compare tools child.

The plugin developer said:
Sometimes your theme files may have the CSS property “overflow” set to “hidden” on some page elements such as sidebars where your mega menu is located.

Check your page source code to see all of the tags that wrap your vertical mega menu and check in the theme’s style sheet for any that may have the CSS rule – overflow: hidden.

But i can’t find anything how to resolve that.

Please tell me how to resolve that.

Thank you very much.