If specifically using the new fully modal interface layout and transitioning to a new map while there are messages visible over the top-left corner of the map, the bottom bar may remain visible and is always red as if it was in the middle of / did not complete fading. See attached image.
It will show there permanently if continuing to play, though restarting the game will of course reset the UI and make it go away. Technically loading a save at the moment there are still messages visible can cause the same effect.
I initially encountered this in my first Beta 13 playtests, and others have seen it since, but there's no way to reliably repeat this (or even frequently repeat it--never pops up while I'm looking for it) and I can't otherwise see how it results from the current architecture, so unless someone can find a truly reliable way to cause it, or any more clues that point to more likely related conditions, I guess it'll just be a thing that can happen...