"KeyNotFoundException" is thrown on trying to restructure children of prefab instance after opening the prefab. Refer the attached video

Steps to reproduce:
1) Create a new project
2) Create three empty gameObjects renamed A, B and C
3) Create a hierarchy such that A is the parent of B and B is the parent of C
3) Create prefabs of these gameObjects
4) Drag C into A > In Restructure window > Open Prefab

Actual Result: "KeyNotFoundException" is thrown on trying to restructure children of prefab instance after opening the prefab

Expected result: No exception should be thrown

Occurring on: 2020.2.0a10, 2020.2.0a7
Working fine on: 2020.2.0a5, 2020.1.0b7

Environment: Both Windows and Mac

Note: 2020.2.0a6 is not available on Saihai