PROBLEM SOLVED!
When I did get back in touch with Nadine, there was great news. Sam and Jack’s relationship had changed significantly! They now slept together and would even groom each other.The messing outside of the litter trays was a thing of the past, both cats were now fastidious users of all three trays, and Nadine said that Jack’s overall demeanor had changed from being a grumpy cat to a happy cat. She had never thought that Jack’s behaviour might be the cause of Sam’s problems, and she also hadn’t realised that Jack was not a happy cat, so this case really was a ‘happily ever after’ for everyone! I reminded Nadine to keep introducing novelty and challenges into the indoor environment for Jack and Sam, and with that, said my goodbyes with a big smile on my face.