I’m having the same problem as everyone else here, in Unreal 4.19
If I open the project file, everything compiles nicely and it all work.
If I move the content to the content folder of a current project in order to add grass etc, it doesn’t work. All the models, textures and so on a delinked and can’t see each other, you just get grey slab trees, grass and so on. None of textures work either.