"All Panels Visible" view not displaying PDFs


I am using EndNote X7.7.1 on Mac.   As of today, when I open a reference, the attached PDFs do not appear in the “All Panels Visible” display option.   When I click on “Preview Panel Not Visible,” the PDF does appears by itself.   Everything was working fine until today. 

Any suggestions for how to get this capability back? 



Usually this is because the border  has been inadvertantly dragged all the way to the edge.  see if you can hover your cursor over the edge and see the move (not sure what that looks like on the mac, but it is two verticals with arrows pointing outward on a pc) and grab and move it to the right?  

This worked.  Thanks very much!