The amount of banding is effected by temperature. If you black cal the camera, then it warms up or the ambient temperature changes significantly, the banding will reappear. Make sure to black cal after the camera has reached a stable temperature, leave it running for about 20 minutes or so in the environment you'll be using it in before use.
For example, letting it warm up indoors, then taking it outdoors where it's cold will cause this to show up.