I have created a custom menu and have positioned it in the "left" and to show only on "selected posts" What I notice is that it only appears when I make my window on the screen very narrow like 25% of the width and in the full screen mode it will show the post moved to the left but will not show the custom menu that i placed in the left position.
You can observe the behavior at
http://ashakiran.com/Jul2017/history/It does not seem to matter if i use a different widget like text, or put it on the right the same behavior repeats.
I have upgraded to the latest version of Vertex.