Reproduction steps:
1. Open the user's attached project "Test2020.zip"
2. In the Project window open Assets/Scenes/SampleScene
3. Select "Doesnt Work" GameObject and expand it
4. Enter Play mode
Expected result: GameObjects that have "/" in their names are found using Transform.Find
Actual result: GameObjects that have "/" in their names are not found using Transform.Find
Reproducible with: 2018.4.28f1, 2019.4.14f1, 2020.1.11f1, 2020.2.0b10, 2021.1.0a4