Yesp I saw it because you used a shortcode same with main menu and it’s getting overlay menu together.
There are two way for the avoid this:
1. Create a new menu for the overlay menu widget contents for example overlay menu and then use this shortcode in to the Overlay menu widgetlike [maxmegamenu location=overlay_menu] etc..
2. You can use static contents in the widget.
You can use these ways and see the clear results. Right now your issue has been fixed but you content not okay in the widget.
I hope those are clear.