Options for Prefab Instance and Prefab Definition object variables don't generate when prefabs are created by dragging and dropping gameObject from hierarchy to project window or if script machine is added as an override

Steps to Repro:
1. Create a new Project
2. Project window > Right-click > Create > Visual Scripting > Script Graph
3. Select Script Graph > Edit Graph > Dock Script Graph window
3. Hierarchy > right-click > create empty
4. Hierarchy > select GameObject > Add Component > Script Machine
5. Drag and drop and attach Script Graph to Script Machine
6. Drag and drop GameObject in the project window to create a prefab
7. Select the GameObject again in Hierarchy
8. Script graph window > Blackboard > Object Variables

Actual Result:
The options for Prefab Instance and Prefab Definition object variable don't generate

Note: Prefab Instance and Prefab DefinitionThe options show for the same GameObject when the project is restarted or when the object is deleted and readded. Very rarely they also show when the script window is closed and reopened.

Expected Result:
The options for Prefab Instance and Prefab Definition object generates in the graph

Reproducible on: 2021.2.0a4, 2021.1.0b5, 2021.1.0b1

Note: Visual Scripting was introduced in 2021.1.0b1

Package Version 1.5.1-pre.3

Environment:
Windows 10, Mac 10.15