Can reproduce, but this isn't the script. When you stroke a path, the brush is centered on the path. If you path has integer coordinates, if falls "between the pixels" so the brush cannot paint fully colored pixels and it has to do approximations. A works around is to put your path anchors on the center of pixels.
But for this specific pattern, it would be much better to stroke in Line mode with a dash pattern, once for the yellow and once for the black.
But for this specific pattern, it would be much better to stroke in Line mode with a dash pattern, once for the yellow and once for the black.