Custom Reflection Probe cubemap is lost when changing Lightmap Encoding

Jira twin of: https://fogbugz.unity3d.com/f/cases/1376533/

Repro steps:

1. Open repro project (ReproRefProbeLost.zip).
2. Open SampleScene scene.
3. Observe that the reflection probe in the scene has a custom cubemap set. It's just a solid red color.
4. Open Project Settings and go to the Player tab.
5. Change Lightmap Encoding setting from High Quality to Normal Quality.
6. Change Lightmap Encoding again from Normal Quality to Low Quality.
7. Observe that the reflection probe in the scene has lost its custom cubemap.

Notes:

• Expected: Reflection probe still has custom red cubemap
• Actual: Reflection probe cubemap has been replaced by a bake of the skybox.
• Reproduces on: 2019.3, 2021.2
• It seems like the project setting must be changed twice for the bug to start appearing.
• Might be skymanager related, not sure.