For grid post featured images, I'm only getting images to show if I set the content to 0 (full content). The 1 (no content) or 2 (excerpt) aren't returning images.
Limit grid post content to ___ characters
Enter 0 for full content. Enter 1 for no content. Enter 2 for excerpt.
My Genesis Theme settings do have featured images checked for Content Archives, but I'm pretty sure this setting is irrelevant for your plugin. I've looked around to see if I have anything else that could be creating a conflict, but nothing jumps out.