Timeline Preview mode locks you in Prefab isolation mode after modifying the prefab... disabling TL preview mode lets you exit the isolation mode.
This bug was introduced/injected by the Prefab Isolation feature.

repro:
- Import attached package
(scene with a Prefab + Timeline)
- Open "IsolationTest" scene
- Select "Main Camera" prefab in the hierarchy
- Open Timeline window & enable Preview mode
- Enter prefab isolation mode on the "Main Camera" prefab
- In isolation, select child Cube and move it (this is important, you MUST edit the prefab)
- Now, click the "Scene" button/icon in the Scene window to return to the scene...
bug: nothing happens.
expected: you should exit isolation mode and return to the scene.

workaround: disable Preview mode in the Timeline window, then click the "Scene" button/icon in the Scene window.