Flutter RouterDelegate: Android back button closes the whole app despite RootBackButtonDispatcher

I am using PopNavigatorRouterDelegateMixin and RootBackButtonDispatcher and I would expect that the back button press would call the onPopPage method of the navigator built in the router delegate. Instead the back button pops the whole app.

This is the app code

 GetMaterialApp(
            navigatorKey: navigatorKey,
            debugShowCheckedModeBanner: false,
            home: Router(
              routerDelegate: AppRouterDelegate(),
              backButtonDispatcher: RootBackButtonDispatcher(),
            ),

and this is the RouterDelegate

class AppRouterDelegate extends RouterDelegate<AppRoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<AppRoutePath> {

  final GlobalKey<NavigatorState> navigatorKey;

  AppRouterDelegate() : navigatorKey = GlobalKey<NavigatorState>();

  @override
  Widget build(BuildContext context) {
    return Navigator(
      pages: [
        if (!context.watch<AppState>().loadingDone)
          MaterialPage(child: LaunchWidget())
        else
          MaterialPage(child: AvailableMatches()),
        if (context.watch<AppState>().selectedMatch != null)
          MaterialPage(
              key: ValueKey("MatchDetails"),
              name: "MatchDetails",
              child: MatchDetails(matchId: context.read<AppState>().selectedMatch)
          )
      ],
      onPopPage: (route, result) {
        print("popping");
        print(route.settings.name);

        if (!route.didPop(result)) {
           return false;
        }

        if (route.settings.name == "MatchDetails") {
          context.read<AppState>().setSelectedMatch(null);
        }

        notifyListeners();
        return true;
      },
    );
  }

  @override
  Future<void> setNewRoutePath(AppRoutePath configuration) {}
}