I think you’re just trying to pick a little too quickly. Sometimes, especially when creating 3D objects, things don’t fully finish happening exactly when you call them, so attempting to use them may not work until a frame or two later. In your case, you are creating the ground mesh and trying to pick from it in the same frame, so I think the ground mesh just isn’t quite finished initializing itself yet. If you do the picking a little later, it works as expected.