Black seams appear between meshes with low 'Texture Quality' and 'Antistropic Textures' settings.

Steps to reproduce:
1) Open the latest attached project (919409-LightMapBug.zip).
2) Enter play mode.

Camera starts moving back and forth. Notice how a seam appears in the middle of the surface in the scene (the surface consists of two separate meshes). The seam gets thinner as the camera moves in.
Increasing 'Texture Quality' and setting 'Antistropic Textures' to Forced On in Quality Settings makes the issue less visible.

The issue can be seen in the Editor as well as in standalone builds.

Reproduced on:
2017.2.0a3, 5.5.1p3

Tested on:
macOS 10.12.6 w/ Metal & OpenGL