I replied to your email and I think you didn't get it. I posted a couple of days ago.
Dan, No worries about response. I am glad you guys are busy. It is so good to see photoshop having serious competition!
I posted the files to dropbox (pic below). Please note, the CR3 files were made at the same time as the fits files (that's what the asiair does). I sent all the files in case it matters. The Lights 3Full Spec includes 2 files taken before the meridian and 3 after so it would be the hardest case as the files are rotated. All the rest line up.
Before sending this email I tried the CR3 files again and they gave me the same message, failure to stack (the same message I got for all 4 folders).
Just to reiterate, I tried Sequator to stack and had no problems. And, I tried 2 earlier versions of Affinity as well as the current (2.5.3) and same problem, failure to stack.
Hope this gives you what you need. I really was surprised to have this problem. For the last 2 years I have used Photo 2 exclusively to stack except when I do nightscapes of the Milky and have to use Sequator to do the foreground correctly. Maybe one day you will add this capability to Photo 2 to handle foregrounds for nightscapes.
Thanks, Andy
And, here is my comment from today:
Hello again,
I thought I should update you. Last night I shot the NA Nebula. I took 18, 10 minute shots and it included a meridian flip. I also took flats. It stacked fine, but these shots were at 600mm using an asi2600MC pro camera. Everything stacked fine so I am guessing the problems had to do with shooting at 90mm.
Anyway I look forward to what you learn.