As a work around, If you can get the image to open in a graphics program, save it as RGB and try again with Kirby. I see you tried Photoshop but give Gimp or Affinity Photo a try. ImageOptim seemed to like it, so maybe try the result of imageoptim in Kirby rather then the source file.
Ive had issues my self with CMYK images in general (not with Kirby, but in general the common libraries used by most CMS system can get a bit funny with CMYK images).
Feel free to send me your source file, i’m happy to have a mess with it.