Scribe sub-menu Z-index problems

Currently working on the root site of a multisite installation running Scribe.

For test purposes, I'm running a menu at the bottom of the header region. This is the default header installed as part of Scribe. Below the header region, is a new region called "Portal Bar" where the exact same menu is also installed.

The menu is a Mega Menu based on the max mega menu plugin. It is placed on the site using a widget in both locations.

The dropdown sub-menu from the Portal Bar menu location is being displayed behind a slider that is running in the "slider" region just below the Portal Bar region - while the dropdown from menu running in the header is visible over the top of the slider, which is the desire behavior.

The first attached screenshot represents the desired dropdown behavior from the menu in the header. The second is a screenshot showing the submenu behind the slider.

I'm not making any sense of this. It's got to be a css issue. Please assist.