In 19.1 try loading a serialized SceneSetup saved to file shows an empty Hierarchy window, if the file was saved with a previous version of Unity.

Repro:

Use e.g this: https://gist.github.com/svermeulen/8927b29b2bfab4e84c950b6788b0c677 to save a scene setup (e.g in 18.3)
Open 19.1 and restore the setup that was saved to disk.

Notice that the hierarchy is not showing any scenes