filament: SurfaceOrientation doesn't duplicate vertices when generating flat normals

Describe the bug I am having two (separate I believe) issues rendering some meshes in Filament. I’m only opening one issue because they are both related to the same mesh type. We generate many meshes of this type, and the issue is not confined to this specific mesh, but all meshes of this type. First, this is what the mesh looks like in scenekit:

Issue 1

The Filament directional lights only illuminate parts of the scene. This is clear if I light the scene with only a directional light. This issue appears in our viewer as well as the sample-gltf iOS viewer. As you can see a large chunk of the ground plane is not illuminated by the light (maybe there is a setting to fix this, but I played with all that seemed relevant)

At first I thought it was maybe an issue on our side with the triangulation, but as you can see in meshlab the ground plane only has two triangles and appear to be unrelated to the illumination boundaries

*** Issue 2 ***

The colors for the mesh are pretty far off from what they are in all other viewers (SceneKit, MeshLab, ThreeJS). In particular they appear to be much less saturated. I have tried adjusting the colors and intensity of the lights but this did not fix it. Here is what it looks like in Filament when I adjusted the directional and indirect lights to be as good as I could make them

To Reproduce

Load this .glb in filament and observe the issues:

house.glb.zip

These were my exact lighting settings:

    math::float3 harmonics[1];
    harmonics[0] = math::float3(1.0f, 1.0f, 1.0f);
    indirect_light_ = IndirectLight::Builder().irradiance(1, harmonics).intensity(24000).build(*engine_);
    if (indirect_light_ == nullptr) {
      throw std::runtime_error("Creating a filament indirect light failed!");
    }
    scene_->setIndirectLight(indirect_light_);

    // Lights and shadows for room mode captures
    utils::Entity light = utils::EntityManager::get().create();
    LightManager::ShadowOptions shadowOptions;
    shadowOptions.shadowCascades = 3;
    shadowOptions.mapSize = 4096;
    shadowOptions.vsm.blurWidth = 120;
    shadowOptions.vsm.msaaSamples = 16;

    LightManager::Builder(LightManager::Type::DIRECTIONAL)
        .color(Color::toLinear<ACCURATE>({0.98f, 0.9f, 0.86f}))
        .intensity(38000)
        .direction({0.2, -1, -0.3})
        .castShadows(true)
        .shadowOptions(shadowOptions)
        .build(*engine_, light);
    scene_->addEntity(light);

Expected behavior A clear and concise description of what you expected to happen.

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Desktop (please complete the following information):

• OS: tested on iOS, Mac, Android and WebGL
• GPU: All tested
• Backend: Tested on OpenGL, Metal and WebGL

Smartphone (please complete the following information):

• Device: [e.g. Pixel 2]
• OS: [e.g. Android Pie 9.0]

Additional context Add any other context about the problem here.