Possible issue in exported interface callback?

[QbProg]

I'm authoring and exporting a C# public interface which I want to implement on the CppWinRT side, then pass it back to C#

public class MyTestUser
{
     public void Test(IMyTest instance) { instance.hello(); }
}
public interface IMyTest
{
    string hello();
}

In cppwinrt I generate an implementation using

struct MyImpl : public winrt::implements<MyImpl, winrt::CSComponent::IMyTest>
{
	hstring hello() { return L"HELLO"; }
};
...
CSComponent::MyTestUser instance; //ok
instance.Test(make<MyImpl>.as<CSComponent::IMyTest>());

doesn't matter what I do (I did a LOT of tests), but the C# side always fails when calling the RCW function (it does generate the wrapper correctly) but it fails in
DynamicInterfaceCastableHelpers.GetInterfaceImplementation
with

System.InvalidOperationException: 'Type 'ABI.CSComponent.IMyTest' returned by IDynamicInterfaceCastable does not implement the requested interface 'CSComponent.IMyTest'.'

Point is that the message is not true, at least at the ABI level the interface is implemented and correctly returned by QueryInterface

The C# test method is correctly invoked and it seems that the interface wrapper is filled. It only fails when calling the interface method.

Is this scenario supported somehow?