CMYK banding appears when returning from photoshop to lightroom.

When you say “CMYK banding,” do you mean the image was converted to CMYK mode in Photoshop, or, do you mean the image is in RGB mode but the banding reminds you of CMYK colors?

If you mean you converted the images to CMYK in Photoshop, Lightroom Classic supports importing CMYK mode images, but from that point on it’s going to work with them in its RGB working space. However, the banding issue seems to be a completely separate issue than CMYK support, because my Lightroom Classic catalogs contain a number of CMYK images that preview just fine with no bands.

So regardless of whether or not the image is in CMYK mode, the colored bands should not be happening, but I’m not sure why they are. When bands like that are seen with camera raw files, it’s sometimes due to corruption during data transfer from the camera card. With that in mind…how do those edited files look in another viewer, such as Apple Preview or Adobe Bridge? In other words, do the bands appear in all viewers, or only in Lightroom Classic? That would help you narrow down whether the problem is at the viewer end, or is being introduced by Photoshop somehow.

It might also help to tell us what format the images are in. For example, are they TIFF files, and if so, which TIFF compression option was used when saving them from Photoshop? Or are they PSD, PSB, JPEG, PNG, etc. files? Sometimes things like that can affect how other software can read them.

You mention 'CMYK' in the title. Did you convert the image to CMYK in Photoshop? Lightroom Classic does not support CMYK, so that may be the explanation.