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

*Repro steps:*
# Open repro project (ReproRefProbeLost.zip).
# Open SampleScene scene.
# Observe that the reflection probe in the scene has a custom cubemap set. It's just a solid red color.
# Open Project Settings and go to the Player tab.
# Change Lightmap Encoding setting from High Quality to Normal Quality.
# Change Lightmap Encoding again from Normal Quality to Low Quality.
# 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* Actual: Reflection probe cubemap has been replaced by a bake of the skybox.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.