How to reproduce:
1. Import user-submitted scene in an empty Unity project (lightmap_error.unitypackage)
2. Open scene "test.unity"
3. Bake lighting
4. Observe floor tiles for sudden changes in color

Expected result: All floor tiles are evenly lit
Actual result: Some floor tiles are noticeably darker than others

Reproducible with: 2017.1.4p2, 2017.2.3p1, 2017.4.6f1, 2018.1.5f1, 2018.2.0b8, 2018.3.0a1

Notes:

• User speculates this issue could be related to Reflection Probes but the same result can be achieved when all Reflection Probes are disabled.
• Cleaning GI cache does not help
• Reflection probe weights get calculated incorrectly and fluctuate greatly when the object is rotated at a very small angle