I believe this is because of the commit here:
e01e2dc#diff-86c1eb8e1ae625825c97d335eaea9712
if(!Application.isEditor) // DontDestroyOnLoad can not be called in editor mode DontDestroyOnLoad(Instance);
When loading a new scene, the AsyncManager instance is destroyed preventing any Await calls to complete.
DontDestroyOnLoad does work in Editor. So not following the reasoning behind the change.