Steps To Reproduce:

1. Create a Project.
2. Turn Off the directional Light.
3. Hierarchy> 3D GameObject > Terrain (0,0,0)
4. Hierarchy > 3D Game Object > Cube( 0, 5, 0)
5. Hierarchy > Light > Spot Light.
6. Position the light in such a way that the light reaches the terrain while falling on the cube.

Actual Result: Cube's shadow doesn't appear on the terrain.

Expected Result: Terrain should receive shadow of the cube.

Reproducible On: 2018.3.0a8, 2018.3.0a4

Not Reproducible On: 2018.3.0a3

Environment: Win and Mac