Summary: Alpha clipped materials attached to flat planes, when angled perpendicular to the light, and if positioned at certain X and Z locations in world space, will cut holes through baked shadows.

Steps to reproduce:

1. Open attached project
2. Open scene "Bug report"
3. Move scene camera to the center of terrain cluster
4. Bake lightmap
5. Notice lines cut out of baked shadow

Reproduced with: 5.2.5f1, 5.3.6p6, 5.4.1p4, 5.5.0b6

Workaround: use the progressive lightmapper or move object closer to (0,0,0).

A fix for Enlighten is to change the push-off parameter to a larger value. An order of magnitude higher pushoff value (0.001) fixes the artifacts on this tree scene.