How to reproduce:
1. Open the attached project
2. Open the "SampleScene" scene
3. In the Hierarchy, select GameObject
4. Duplicate the GameObject (CTRL + D or CMD + D)

Actual result: Unity freezes or crashes.
Expected result: The Game Object is duplicated.

Reproducible with: 2018.4.2f1, 2018.4.12f1, 2019.2.11f1, 2019.3.0b9, 2020.1.0a11.
Regression introduced in: 2018.4.2f1.
Not reproducible with: 2017.4.33f1, 2018.3.14f1, 2018.4.1f1.

Notes:
- Unity 2020.1.0a11 duplicates the item at first, throws failed assertion and freezes on second duplication.

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Fixed in 2020.1.0a15, 2019.3.0f3.