How to reproduce:
1. Open "1242829_Lightmapper" project
2. Observe the Sphere GameObjects in the Scene view
3. Go to Window -> Rendering and press Lighting Settings
4. Under Lightmapping Settings change the Lightmapper to Progressive CPU
5. After baking is finished observe the Sphere GameObjects again in the Scene view

Expected result: Both Sphere GameObjects stay lighten
Actual result: One Sphere GameObject becomes very bright, the other becomes black

Reproducible with: 2017.4.40f1, 2018.4.22f1, 2019.3.13f1, 2020.1.0b8, 2020.2.0a10

Note: URP was used in this example for better representation of the very bright GameObject, in built-in it is hard to see the difference, but the issue is present in built-in as well.