Generic method for verifying whether a mocked method called

I am building generic test helper method to verify whether a method is called in the mock with the given type. In my example I am mocking IMediator from the library MediatR. For mocking I am using Moq library

Let's see the code. For the sake of simplicity I made a "dummy" service and a corresponding test, to only focus on the problem. My production code:

public class Service
{
    private readonly IMediator _mediator;

    public Service(IMediator mediator)
    {
        _mediator = mediator;
    }

    public void SendQuery()
    {
        _mediator.Send(new GetAllProductsQuery());
    }
}

And the corresponding test:

    [Fact]
    public void  WhenSendQueryCalled_ThenGetAllProductsQuerySend()
    {
        //Arrange
        var mockedMediator = new Mock<IMediator>();
        var service = new Service(mockedMediator.Object);

        //Act
        service.SendQuery();

        //Assert
        CheckThatRequestSentViaMediator<GetAllProductsQuery>(mockedMediator);
    }

    private void CheckThatRequestSentViaMediator<TRequest>(Mock<IMediator> mockedMediator) where TRequest : class
    {
        mockedMediator.Verify(mock => mock.Send(It.IsAny<TRequest>(), It.IsAny<CancellationToken>()), Times.Once);
    }

My assert method does fail, unexpectedly, with the following reason:

Moq.MockException: 
Expected invocation on the mock once, but was 0 times: mock => mock.Send(It.IsAny<GetAllProductsQuery>(), It.IsAny<CancellationToken>())

Performed invocations:

   Mock<IMediator:1> (mock):

On the other hand, If I specify the type directly in the verification method, the test passes. The passing assert method looks as the following:

    private void CheckGetAllProductsQuerySentViaMediator(Mock<IMediator> mockedMediator)
    {
        mockedMediator.Verify(mock => mock.Send(It.IsAny<GetAllProductsQuery>(), It.IsAny<CancellationToken>()), Times.Once);
    }

It looks quite strange to me, since the second assert method works flawlesly. But if I use the generic type parameter and pas it on to the verify method, it fails. What am I doing wrong? Am I not aware of some important underlying behaviour of C#/.NET.Core? Thanks for the help!