JPEG to RAW introduces lines

Using JPEG to RAW to make a sky smooth – but it introduces vertical lines in the output. The image is an old 2MP image – these artifacts are not apparent in the original. I’ve also run the image through Gigapixel and then through JPEG to RAW, and I get similar lines. How can I avoid these terrible artifacts?

Try using CPU/OpenVINO mode instead of GPU. And please provide technical info of your PC, it saves time.