Flutter Riverpod always one state behind / delayed

I have a drop-down where I can select several items. I am using a StateNotifier because the logic is a little bit too complicated for a simple StateProvider. I have a model class with attributes I want to fill e.g.

Class ReportError {
Name;
Code; 
Png;
...
}

So here is my problem:

@override
Widget build(BuildContext context) {
  final selectedValue = ref.watch(fillErrorModelProvider).selectedTool; //here I watch at my state, here I think is my problem
  return Stack(
    children: [
      Align(
        //..Here is my drop-down on changed
        onChanged: (value) {
          ref.read(fillErrorModelProvider.notifier).setToolName(value!);
                                  print(selectedValue); // and this is always one behind. So when I select cat, it says null, then I change to dog, it says cat.
        },
      ),
      //...
    ],
  );
}

What am I doing wrong? According to the documentation I thought I have to do this Variable = ref.watch(provider) directly under the build method.
When I change the print statement to the ref.watch directly, everything works fine.
My provider stuff:

final fillErrorModelProvider = StateNotifierProvider<FillReportBugModelNotifier, ReportBugModel>((ref) {
  return FillReportBugModelNotifier();
});
class FillReportBugModelNotifier extends StateNotifier<ReportBugModel> {
  FillReportBugModelNotifier() : super(ReportBugModel());

  void setToolName(String selectedTool) {
    state = ReportBugModel().copyWith(selectedTool: selectedTool);
  }
}