How to reproduce:
1. Open the attached (Repro.zip) project
2. Open the "test space factorio white" Scene
3. Expand the "_DefaultSceneRoot" Prefab -> select "volume" GameObject
4. In Inspector Window press "Add Override" and add any overrides
5. Save the project -> Reopen the project -> check the "volume" GameObject (there are "Before reopening" and "After reopening" pictures attached)

Expected result: All added overrides are still there after reopening the project
Actual result: All overrides are gone after reopening the project

Reproducible in: 2019.3.1f1 [HDRP 7.0.1], 2020.1.0a23 [HDRP 7.1.8]

Notes:
- Could not test on 2019.2 and lower versions, because Volume Framework does not exist in these versions
- When adding overrides in simple GameObject with Volume (which is not inside the Prefab) - they still appear after reopening the project