Loading a new scene additively automatically loads inactive scenes

Question

I am trying to load a new scene while maintaining an inactive scene inactive. I have three scenes. The "Main" scene, the "Options" scene and the "Heavy" scene. The game starts on the "Main" scene and the "Heavy" scene is loaded async and remains inactive like this:

SceneOperation = SceneManager.LoadSceneAsync("Heavy", LoadSceneMode.Additive); 

SceneOperation.allowSceneActivation = false;

Then I load the new "Options" scene additive, like this:

SceneManager.LoadScene("Options", LoadSceneMode.Additive);

When doing this, the "Heavy" scene suddenly becomes active even though allowSceneActivation is set to false. I have tried changing the "Heavy" scene loading to single, but it doesn't fix the issue:

SceneOperation = SceneManager.LoadSceneAsync("Heavy", LoadSceneMode.Single); 

SceneOperation.allowSceneActivation = false;