AsyncOperation for SceneManager.LoadSceneAsync doesn't adhere to Application.backgroundLoadingPriority

I’m loading levels with:

AsyncOperation async = SceneManager.LoadSceneAsync()

I’ve set background loading priority via:

Application.backgroundLoadingPriority = ThreadPriority.Low;

According to Unity - Scripting API: Application.backgroundLoadingPriority, setting ThreadPriority.Low - 2ms “This is a maximum time all asynchronous operations can spend within a single frame on a main thread.”

However, I’m seeing huge performance hits when scenes are loading… here we see 123ms spent loading:

Any clues why this AsyncOperation is not following backgroundLoadingPriority? Or how to REALLY load the scene asynchronously without the performance hit?

AsyncOpertion.priority does not take the ThreadPriority enum

The load/unload Scene thread is always high priority, all you can do is change which SceneLoad-job may be executed first.
The default value is 0 and any higher value will equal a higher priority.