WPF INotifyPropertyChanged two way binding strange action

Question

I implemented INotifyPropertyChanged as recommended by many threads.
Implementation 1

public class Notifier : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public void OnPropertyChanged(string pName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(pName));
    }
}

public class Model : Notifier, IDataErrorInfo
{
    private string name;

    public string Name
    {
        get { return name; }
        set { name = value; OnPropertyChanged("name_changed"); }
    }
}

And the viewmodel consists of the model and command to make changes to model properties.

public class ViewModel : Notifier
{
    private Model _model;

    public Model Model
    {
        get { return _model; }
        set { _model = value; OnPropertyChanged("model_changed"); }
    }

    private ICommand _cmd;

    public ICommand Command
    {
        get { return _cmd; }
        set { _cmd = value; }
    }

    public void ExecuteCommand(object para)
    {
        Console.WriteLine("Command executed");
        Model.Name = "new name";
    }
}

VM is then binded to the view.

<TextBox HorizontalAlignment="Center" VerticalAlignment="Center"  Width="100">
    <TextBox.Text>
        <Binding Path="Model.Name" Mode="TwoWay" NotifyOnValidationError="True" UpdateSourceTrigger="PropertyChanged" ValidatesOnDataErrors="True">
            <Binding.ValidationRules>
                <ExceptionValidationRule></ExceptionValidationRule>                
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

When the command is executed, the TextBox does not get updated to new value.
However, if I implement the INotifyPropertyChanged like this instruction, the binding works.
Implementation 2

public class Notifier : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected bool SetProperty<T>(ref T field, T newValue, [CallerMemberName]string propertyName = null)
    {
        if (!EqualityComparer<T>.Default.Equals(field, newValue))
        {
            field = newValue;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
            return true;
        }
        return false;
    }
}

public class Model : Notifier, IDataErrorInfo
{
    private string name;

    public string Name
    {
        get { return name; }
        set { SetProperty(ref name, value); }
    }
}

What is missed in the first method?

Answer 1

Please add property name like this.

public class Model : Notifier, IDataErrorInfo
{
    private string name;

    public string Name
    {
        get { return name; }
        set { name = value; OnPropertyChanged("Name"); }
    }
}