Is there anyway you can run with app with Xcode? I am not familiar with Xamarin Forms, but if they export an Xcode project, can you run that on the simulator and see where the crash is happening? If not, you might have better luck checking Xamarin Form's website/forum for your problem.

I found a work around. In the detail view, I don't edit the grouping field directly and instead use a @State var to edit the grouping field. Then I hide the back button and use a custom back button, that will set the grouping field right before I dismiss the view. That way the view stays in place until they hit the back button. Is there a better way to do this?