We are experiencing a z-index bubbling issue on all upfront themes on the mobile navigation. We have tried this on several sites with the same result. Items under the mobile menu are still clickable when the mobile menu is open. The easiest way to see this is when closing the mobile menu when the open menu is right underneath close mobile menu icon. The experience is that every time you try to close the menu it reopens.
This is not testable in a desktop browser in mobile view. It has to be tested from a smartphone.
We had reported this when we first started using upfront about a year ago and was told it was a bubbling issue, but believed it was something we had done wrong. After testing this on all upfront themes and some custom ones we have made, we are starting to believe that the issue is in the implementation of the triggered menu in upfront.