I had the same issue and did not receive a solution, just to check the CSS. So after wading through that, I hope this doesn’t come too late! I had to go in to the plug-in editor, go to the wp-listings/includes/wp-listings.css file and locate the following line of code: (should be near the top)
‘img{margin:0;padding:0;width:100%;height:auto%;border:none}’
When I changed the height to 100%, the problem was resolved.
Again, hope this is not too late but I went through lots of support questions trying to find a solution to this problem so I wanted to share what worked for me!