Loading Lights from USD in SceneKit

Problem: No Lights get imported from USD into my Scene (Geometry, Cameras and Materials worked flawless so far).

I am using ModelIO to load a USD Scene (testing both usd and usdz) created in Blender, Cinema4D, Houdini or Maya (Testing all to see if at least one of those will output something working). Scenes got cross-checked in each tool and usda reviewed manually, at least the lights in scenes from blender and maya seem to be exported correctly.

I am using both ModelIO and SceneKit directly to load the scene (see the two sections in my example code). SceneKit-Documentation claims that the lights are supported (See Validating feature support for USD files; Using DistantLights and SphereLights).

Example of my loading code:

    let testScenePath = mainBundle.path(forResource: "Maya", ofType: "usdz")
    let url = URL(fileURLWithPath: testScenePath!)

    // case 1: code used if loading with scene kit directly (simplified, ommiting try/catch)
    let scene = ScnScene(url: url)

    // case 2: code used if using Model I/O to load usd
    let mdl = MDLAsset(url: url)
    let scene = SCNScene(mdlAsset: mdl)