When it comes to missing images there's a few things that can happen.
One, we don't currently synchronize images. So if Turn 14 added a new image after the product was created we currently have no way of adding it. (This is something we are working on.)
Two, occasionally there can be an error while loading the image, you could always delete the product and allow the app to reload it and see what happens. (Or you can do this brand by brand.)
Three, sometimes Shopify rejects the image if it's the wrong size or other issues like that.
Four, there are what we refer to as blocked brands. These are brands that due to either licensing or copyright issues wont allow Turn 14 to share their images. They can use them on the Turn 14 site, but can't distribute them. This is an issue they are aware of and do work to improve.