My vertical submenu does not remain expanded after click on some submenu items.

It remains open when clicking some items but for some reason when clicking some submenu items it will not remain expanded to display all the sub-menu items.

What is going wrong here?

My vertical submenu does not remain expanded after click on some submenu items. It remains open when clicking some items but for some reason when clicking some submenu items it will not remain expanded to display all the sub-menu items. What is going wrong here?