Reproduction steps:
1. Open linked Project
2. Open Assets\\Scenes
bug Scene
3. Select PROBLEM_OBJECT in the Hierarchy
4. Expand Game Mode in the Inspector
5. Select the Object in the Modifier field
Expected result: The Object is selected
Actual result: The Editor crashes
Reproducible with: 2019.4.24f1, 2020.3.5f1, 2021.1.5f1, 2021.2.0a15