Mock is returning null after constructors is called

Question

I want to mock the hidden property Identity, but MyChannelMock.Object.Identity is null after constructor is called.

The class looks like this:

public abstract class CommunicationRouter<TChannelType>
where TChannelType : class, ICommunicationChannel
{ 
  protected readonly Mock<TChannelType> MyChannelMock;
  protected CommunicationRouter()
  {
        MyChannelMock = new Mock<TChannelType>();
        // object that's not null
        var identity = new SomeIdentity();
        // 1st method I've tried to mock but return is null
        MyChannelMock.Setup(_ => _.Identity).Returns(identity);
        // 2nd method I've tried to mock but return is also null
        MyChannelMock.As<ICommunicationChannel>().Setup(_ => _.Identity).Returns(identity);
  }
 }

interface ICommunicationChannel
{
    public MyType Identity{get;set;}
}

interface ICustomChannel : ICommunicationChannel
{
    public new MyType2 Identity{get;set;}
}

I can not find the problem of this mock nowhere, so I'll appreciate if u can give me any others tips.