Upload & Sell: Off
Okay, but it's not outside the realm of possibility that the camera is writing the previously processed image to the card while it's starting to process the next shot. If there's a hiccup writing to the card, it's theoretically possible that it's corrupting the processing of the next shot (which would also impact the JPEG.)
Outside of the card, the only other item you really have control over is the battery...and I doubt that's it. Not sure there is much you can do, especially if you sent it back and got another. If it's an issue across all cameras, then maybe there will be a firmware update coming. I've never run into this so I've been lucky. If it's finicky about SD cards, then I would expect that some people would run into the issue and some may not....hence the suggestion. It very well be a wild goose chase though.