The answer is that I honestly don’t know exactly what worked in the end. They rejected it three times for the same issue: The window has been marked as needing another Layout Window pass, but it has already had more Layout Window passes than there are views in the window.
I was getting worried about the number of rejections and didn’t want to keep trying and getting rejected in case they got fed up, so I spent half a day cleaning up paint events and working hard at only refreshing when absolutely necessary and only the areas that needed refreshing etc etc etc. Something worked as it was finally approved in 6 minutes during the fourth review.