I think it's linked to the alpha channel problem. It seems like when importing an image you lose a lot of the alpha value for anything that's not totally opaque. When you export you lose it again. In my case I had a blob with a body that was 50% opaque and shadows that were 75%. When importing it to Juice FX, I lost the body completely and the shadows were faint. When I exported I lost all the shadows too and was left with only the outline.