可能的原因是需要处理注册失败的情况，并从 AmplifyException 中获取错误信息。可以添加一个错误处理程序并在用户注册出现错误时显示错误消息。

示例代码：

try {
  final authResult =
      await Amplify.Auth.signUp(
          username: emailController.text.trim(),
          password: passwordController.text.trim(),
          options: CognitoSignUpOptions(
              userAttributes: {'email': emailController.text.trim()}));
  // handle successful signup
} on AmplifyException catch (e) {
  print('Failed to register user - ${e.message}');
  scaffoldKey.currentState.showSnackBar(
      SnackBar(
          content:
          Text('Failed to register user - ${e.message}')));
}