Return dotnet variable from dll wrapper

Hello,
I've created a dll which is a wcf wrapper, and a function in this dll which returns an custom object defined in this dll also.
Its NAV 2016, code looks like:

MyWrapper := MyWrapper.Wrapper();
ReturnedObject := MyWraper.Function(parameters);

My problem is that ReturnedObject and its properties remain uninitialised after the function call, what breaks further code flow.

Earlier int the code i call other function from wrapper which returns string - that works completely fine.

Is there a way to retrieve custom objects like this?

Returned object class has attribute

Serializable

but this does not help.

Thanks for any suggestions!