How to reproduce:
1. Open the attached project
2. Open the "SampleScene.unity" scene
3. Press Play
4. Once you see SampleScene appearing in the Hierarchy, pause the Play mode (to prevent Unity crashing)

Actual result: Unity randomly adds SampleScene to the Hierarchy.
Expected result: Unity shouldn't add any scenes into the Hierarchy.

Reproducible with: 2019.2.0a8, 2019.2.0a1, 2019.1.0b6, 2019.1.0a11.

Notes:
Sometimes Unity may crash before the SampleScenes are added to the Hierarchy. (The crash is reported)
Errors are thrown when selecting the scenes in the Hierarchy.