I'm getting artefacts on stacked images. They mostly appear on filters used at the start or end of the session when the seeing conditions are poor and there is light pollution. At present, there is no true darkness where I am (just twilight). I have cleaned the glass in front of the sensor but the pattern remains exactly the same. Attached is an image. Does anyone recognise this pattern and should I be concerned and take remedial action? The stacks do mostly result in a reasonable final image. I've not tried imaging during perpetual twilight with a bright Moon around before so the issue could simply be this.
