Steps:
1. Add Cube to the Hierarchy and convert it to Prefab
2. Select instance and remove Mesh Renderer component
3. Add child GameObject to Cube prefab instance
4. Select Cube instance and revert all through Overrides window
5. Undo
6. Redo
==>
"Child GameObject 'GameObject' was not registered into undo system and became dangling during an undo operation" warning appears

Not reproducible: 2021.2.0b13.3550
Reproducible: 2022.1.0a15.2209