The retina image works intermittently. I've tried uploading all shapes, sizes, and image types, using the resize feature, but I run into the same issue on my iPhone 6 and older iPad. Sometimes the higher res image loads, but other times only the lower res image loads then quickly goes to a text only square. Is this a know issue that you're working on? Or is there a file type, size, setting that will fix this?
Also, only seems to be a problem on the home page. All other pages don't seem to have a problem loading the retina image.