How to reproduce:
1. Open the attached project
2. Select Resources/Gem.prefab in the Project
3. Press "Open Prefab" in the Inspector

Actual result: Unity crashes.

Reproducible with: 2019.2.0a9, 2019.1.0b8, 2018.3.9f1, 2018.3.0b1.
Regression introduced in: 2018.3.0b1.
Not reproducible with: 2018.3.0a7, 2018.3.0a11.

Notes:
Some failed Assertions are thrown:
Assertion failed on expression: '!(m_Object.find(fileID) != m_Object.end() && m_Types[m_Object.find(fileID)->second.typeID].GetPersistentTypeID() != objectPersistentTypeID)'

The project may crash on import, in that case, delete all folders except "Assets" in the project directory.