Bug: Filter/Sort pop-up appears behind comments sidebar

The filter and sort pop-up menus appear behind the comments sidebar instead of on top of it. The user has to slide the sidebar to see and interact with the pop-up. This occurs in both Chrome and Safari and is independent of the browser window size. This is likely a z-index regression from the recent Advanced Comment Search & Filter update. [REF-RESEARCH:EVHFKH]