How to reproduce:
1. Open the “PrefabTest.zip“ project
2. Open the “SampleScene“
3. Open the “Assets/Canvas.prefab” Prefab in the Project tab
4. Observe the “Canvas“ GameObject in the Hierarchy
5. Exit the Prefab Edit Mode
6. Select the “EditorButton” GameObject in the Hierarchy
7. Click on the “Prefab Load/Save“ Button in the Inspector
8. Select and open the “Assets/Canvas.prefab” Prefab in the Project tab
9. Observe the Hierarchy

Expected result: The Canvas has not changed
Actual result: The Canvas has a grayed-out “Canvas (Environment)“ root GameObject

Reproducible in: 2021.3.42f1, 2022.3.30f1, 2022.3.42f1, 6000.0.15f1
Not reproducible in: 2022.3.29f1

Reproduced on: Windows 11 Pro (23H2), macOS 14.5 (by the reporter)
Not reproduced on: No other environment tested

Notes:
- Reproducible only with the Canvas GameObject
- The reporter states that this bug could be caused by the fix of this issue: https://issuetracker.unity3d.com/issues/the-prefab-scale-values-are-set-to-zero-when-the-prefab-with-a-nested-canvas-is-modified-through-a-script