Strange socket behaviour on HeroFPP_Skeleton from FPS Sample

I can successfully add socket to the AnimStarterPack AP_Character, and attach a mesh in my Level Blueprint.

If I follow the exact same steps using the HeroFPP_Skeleton, I get strange behaviour, like the mesh is attached to some random point below the skeleton?

Any ideas why there should be issues with the HeroFPP_Skeleton?

BTW - Why is the gun in this sample part of the mesh - wouldn’t that make sense to demonstrate using a socket?