Putting a prefab without unpacking causes hanging up the avatar build

[logicmachine]

How to reproduce

• Create new avatar project
• Import the attached unitypackage: ndmf-build-hangup.zip
  • It contains a plugin that instantiates a prefab
  • The prefab contains a non-transform component
• Open example scene
  • (Menu) -> VRChat SDK -> Samples -> Avatar Dynamics Robot Avatar
• Press the "Build & Test" button
• Build procedure hangs up in PrefabUtility.SaveAsPrefabAsset() called from VRCSDK
  • It doesn't happen always but often.

Environment

• NDMF v1.2.0
• VRCSDK v3.4.0
• VRChat Creator Companion v2.1.4

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It seems that unpacking prefabs prevents this problem. (Unfortunately, I don't know why it works.)
I think this is caused by VRCSDK or Unity, but adding a workaround or notice in the document will be helpful for developers.