I just wanted to say that I have same problem, but it occurred now after a migration between hosts. I have GD installed and everything seems to be working.
I can only see the thumbnails but not the featured image of products in the front-end, but in the back-end I can actually see both the featured image and the image gallery.
The media library is working and i don’t think there are any problems with paths since I didn’t change the domain name.
