What is the exact error message you get when you attempt to debayer the image in PixInsight? In my experience, PixInsight will attempt to debayer any greyscale image, whether it is a CFA image or not. If you get the error “Unable to acquire CFA pattern information”, it means you need to select the Bayer pattern in the PixInsight Debayer process because it is not found in the image header information. I believe this is normal for FITS files acquired with SGP.
Let me clarify my reply above. PixInsight will attempt to debayer any greyscale image IF you ask it to debayer - either by checking “CFA images” in Batch Preprocessing or by running the Debayer process. Both of the images in your screen capture are greyscale, as indicated on their title bars, so if you ask PixInsight to debayer them, it will attempt it. You will need to specify the Bayer pattern (e.g., RGGB) if the image file header does not include it.
@DonR - There is no error message. The process either through batch processing or manually debayering the images (and selecting a bayer pattern) works normally for the images from the first night.
If I debayer the image from the second night the colour space changes from greyscale to RGB but the image stays greysale.
@entilza - First image loaded is the “broken” one, second image is one that debayers correctly.