Scene has dependency to other scenes

Questions & Answers
1

I am creating assetbundles for my scenes.
I have an assetbundle with a few scenes (app1) and another with different scenes (app2).

When I look at the dependencies of the assetbundles app1 has a dependency to app2 (but not the other way arround). And if I check each scene from app1 (right-click Select all dependencies) there are 2 scenes that have dependencies to all the scenes of app2.

How is it possible to have a dependency to another scene? I have no idea where to begin looking.
Any help, tips, hints would be appreciated.

2

There were 2 missing scripts on a prefab that was in the scene, but the prefab was not connected anymore so I did not notice it. I removed the 2 scripts from the prefab itself and the dependencies were gone.

Anyone has an explanation for this behaviour?