In the sample project we have a Widget Blueprint asset (SomeWidget) that implements a native interface (PrintSomethingInterface.h). However, in the DefaultEditor.ini file, we've also excluded all Widget Blueprints from being nativized. The end result is that we have a nativized Blueprint asset (SomeActor) that is set up to call one of the interface functions on an instance of the (non-nativized) Widget Blueprint at runtime.
In this case, the generated C++ code for the nativized Blueprint asset is failing to resolve the interface address at runtime, and the implemented function is not able to be called as a result.
Suggested workarounds include:
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-92640 in the post.