Update-
I managed to get a lab appointment with WWDC. Thanks very much to the Apple people who helped me. It took a large part of the 30 minute appointment but they found a solution.
Further to the code that I posted above the List was enclosed in a Section (you can see where I commented // End Section above). Removing the Section made everything work.
I still don't know why it worked on macOS but at the moment I am just happy that it is working on iOS as well.
Thanks for taking the time to look, those of you that did, and maybe I could be a pointer for others who keep searching like I had been.
