How to reproduce:
1. Open the user's attached "USD-ParentTransform" project
2. Open the Scene "SampleScene"
3. In the Hierarchy select the "Luchs" GameObject
4. Export Selected as USDZ (USD->Export Selected as USDZ)

Expected results: The Prefab is exported succesfully
Actual results: The Prefab isn't exported and "Setting the parent of a transform which resides in a Prefab instance is not possible" error is thrown

Reproducible with: 1.0.3-preview.2 (2018.4.30f1, 2019.4.17f1, 2020.1.17f1, 2020.2.0f1, 2021.1.0a10)
Could not test with: 2021.1.0a6, 2021.1.0a10 because of the CS0246 and Cs0115 errors

Notes:
- Unpacking the Prefab and exporting works
- Removing the Animator Component from the Prefab's child lets you export it
- Sometimes "ArgumentNullException: Value cannot be null." error can be thrown instead