Ah! If adding a simple dummy class isn’t working then it makes me suspect environment issues unrelated to the project.
Can you post the “Output” logs of Visual Studio instead of the error list? For Unreal projects Visual Studio’s error list is not usually accurate, the compilation output from the Unreal Build Tool is what we’re really interested in here.
In the meantime, if someone else can try packaging and tell us how it goes that would really help! I think most people have the old v1 version (where packaging definitely won’t work) so if anyone wants to give it a try make sure you download the latest version v1.1 first.
I downloaded the sample project from scratch, tested packaging and it just works for me (even without the C++ class workaround) so I’m beginning to suspect this is more environment related.