It is getting weird. Sometimes I must change the bayer to Set All to Mono and then stack, but it gets the same pattern, then change bayer back to Auto and restack. Sometimes I get the same bad pattern, sometimes it works. When it does not work, sometimes checking the noise reduction box makes it work. There does not seem to be a pattern I recognize in the error and correction process.
Here is M33, 6 x 60 seconds each stacked when it works.
And here is the error, with a very odd histogram
