Edit: Probably nevermind. After restarting Unity, this stopped happening. Perhaps some PBS component was not cleaned up in memory, and was throwing this. In any case, this isn't happening anymore in the scene it was happening in prior to restarting Unity. I have one scene in which the following error gets thrown upon entering play mode: Code (CSharp): SerializedObjectNotCreatableException: Object at index 0 is null UnityEditor.Editor.CreateSerializedObject () (at <d4ac95dcd11e4742ab912a6127ca6eb7>:0) UnityEditor.Editor.GetSerializedObjectInternal () (at <d4ac95dcd11e4742ab912a6127ca6eb7>:0) UnityEditor.Editor.get_serializedObject () (at <d4ac95dcd11e4742ab912a6127ca6eb7>:0) UnityEditor.ProBuilder.ProBuilderShapeEditor.OnEnable () (at Library/PackageCachefirstname.lastname@example.org/Editor/EditorCore/ProBuilderShapeEditor.cs:57) What's strange is that this scene contains no ProBuilderShape components, neither before nor after entering play mode. When trying to debug this, I'm not seeing any clues as to what object is causing this: This is only happening in one scene so far, and it's an editor-only thing, so not really a big deal. But I'd like to understand what's causing this. This is using PB 5.0.3. Any ideas?