Hi, I've been having a similar problem with the thumbnails as other people in this forum: some of the posts use a default image, some don't show an image at all, and some work just fine. All of the images were uploaded (via the WordPress default media uploader) the same exact way. I've been trying to see if something about the images themselves were causing the problem, but I can't seem to distinguish a working thumbnail from a broken one.
My site is: etrethegirls.com
P.S. I already sent an email to the plugin's support team.