UPDATE FROM MABULA
I have had a very rough 2 months unfortunately health wise. I was struck 3x in a row with bacterial infections. The second infection occurred  after a routine hospital checkup and I became very sick. I had to rest and take a lot of antibiotics. Once I was recovering and restarting work 1 month ago, I again became sick. The infection was not yet gone, so even more antibiotics and rest was needed. Needless to say, it took a lot of my energy and I needed a lot of rest.
Finally, the infection is really gone and my energy is coming back step-by-step now and I have started work again. I am terribly sorry to have kept you waiting for support. I will address all outstanding questions and e-mails step-by step and will be on the forum daily from today.
APP 2.0.0-beta47 will come soon as well, a lot of work was already completed before I became very ill, so the release is also nearly ready for you. Beta47 will be much faster actually. Many workflows will be more than 2x faster, mosaics can even be 10x faster than before because registration really received a major boost... all compared to beta46. Â Before I release it, I will make sure that everything is working properly and then I will release it.
When I have been using the light pollution tool recently on my Mac, (I have the latest software, the latest APP.)
I get this strange artifact, anyone seen this or have any advice, thx
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Have you tried running a stack without any calibration files to see if the artifacts remain?
I have seen an effect similar to this in the past. But, as I recollect it occurred only when I used the light correction tool on an image that had already been light pollution corrected. Basically the effect is called posterisation.
When APP runs the LPC tool it produces a color correction model that attempts to flatten out the color gradients in the source image. Assuming selection boxes are well placed the tool provides an excellent (but inevitably somewhat imperfect) result.
When the process is repeated, the selection boxes will be placed somewhat differently and the tool will produce a revised color correction model that attempts to flatten out these minor residual variations. Inevitably however there will still be minor residual color variations in the darkest areas.
The posterisation problem occurs when APP is asked to display the highly-flattened 32 bit resolution image produced by the LPC tool, highly stretched, on a computer monitor only capable of displaying color at much lower resolution. The result is the very minor residual color gradients in 32 bit resolution image start to show as steps at the lower resolution of a color image.
So basically I think nothing is really wrong with your image.
Mike
