Flutter platform specific plugin - Reply already submitted

Question

I am trying to call multiple methods from my platform specific plugin and I am having hard time with errors E/MethodChannel#fuzzy_plugin( 3277): Failed to handle method call E/MethodChannel#fuzzy_plugin( 3277): java.lang.IllegalStateException: Reply already submitted

The code of a plugin is:

class FuzzyPlugin {
  static const MethodChannel _channel = MethodChannel('fuzzy_plugin');

  static Future<String?> get platformVersion async {
    final String? version = await _channel.invokeMethod('getPlatformVersion');
    return version;
  }

  static Future<List<String>> fuzzySystems() async {
    final List<dynamic>? systems =
        await _channel.invokeListMethod("getFuzzySystems");
    return systems!.cast<String>();
  }

  static Future<bool> load(String json) async {
    final bool success = await _channel.invokeMethod("load", {"json": json});
    return success;
  }
}

The methods called in java are

  @Override
  public void onMethodCall(@NonNull MethodCall call, @NonNull Result result) {

    switch (call.method){
      case "getPlatformVersion":
        result.success("Android " + android.os.Build.VERSION.RELEASE);
        break;
      case "getFuzzySystems":
        result.success(FuzzyLibraryController.getInstance().getFuzzySystems());
        break;
      case "load":
        String json = call.argument("json");
        FuzzyLibraryController.getInstance().load(json);
        result.success(true);
        break;
      default: result.notImplemented();
    }

  }

and the method in which i test the plugin is in separate flutter project, android app with next statement

Future<bool> b = FuzzyPlugin.load("working json file, tested");

b.then((value) => () {
      Future<List<String>> fs = FuzzyPlugin.fuzzySystems();

      fs.then((result) {
        print(result);
      });
    });