After I upgraded to plugin version 1.9.5, the plugin quit finding the images in the post to use for the thumbnails (it shows the default image). If I set "featured image", it does find the image instead of showing the default. But, before, we didn't have to set a featured image.
Each post only has 1 image. This has happened for posts I create after the upgrade as well as for the old posts.
Other than that I love the plugin.