How to reproduce:
1. Open attached Unity project "NewGITest01"
2. Load scene "sample"
3. Wait until generating lighting is finished
4. Zoom in Scene view until darker line between cubes appears (in different versions this line appears between different cubes)

Expected Result: There is no visible separation between cubes.
Actual Result: There is darker line between two cubes (case_964180-UnityEnlightenBugReport1a.PNG). In different versions this line appears between different cubes.

Workarounds:
* Remove "CubeGround" object;
* Change Lightmapper to Progressive.

Reproduced with: 2018.1.0a3, 2017.3.0b8, 2017.2.0p1, 2017.1.2p2, 5.6.4p2, 5.5.5p1.

Note: This issue is visible on the Baked Lightmap (case_964180-UnityEnlightenBugReport1b.PNG).