How to reproduce:
1. Open the attached project named "Case_1230405"
2. Open the SampleScene
3. Observe that cubes with static lightmaps are rendered with artifacts
4. Click Tools > ProBuilder > Editors > Open Lightmap UV Editor
5. Observe the warning that there are 3 meshes missing Lightmap UVs
6. Build the missing UVs
7. Generate the Scene Lighting
8. Reload the Scene

Expected result: All meshes have their lightmap UVs and are rendered without artifacts
Actual result: The meshes with static lightmaps have artifacts again and are missing their UVs

Reproducible with: 2018.4.20f1, 2019.3.8f1, 2020.1.0b4, 2020.2.0a5
Could not test with: 2017.4.38f1(No package manager)

Reproducible with package versions: 4.3.0 - preview.2, 4.3.0 - preview.6
Not reproducible with package versions: 4.1.0, 4.3.0 - preview.1