They are not nanite meshes. Neither is the landscape but it generates properly if I turn off the pcg graph.
I find nanite to be kind of garbage at the best of times. When I turned it off I had a massive performance improvement across my entire project. Of course I had to manually optimize all of my models but it was definitely worth it.
Is there not an alternative to nanite? Like if I started a new project from the default Unreal projects, reflections would show up properly.