Steps to repro:

1. Open attached project and 't1' scene;
2. Open Occlusion tab (Window -> Occlusion Culling);
3. In Inspector open Vizualization tab by clicking on it;
4. In the Scene view zoom in closer to trees that are not culled by scrolling mouse wheel.

Expected result:
Shadows are rendered in Scene View for trees that have not been occluded by culling. See attached expected.gif video.

Actual result:
When zooming closer to trees their shadows disappear from Scene view.See attached actual.gif video.
Regression introduced in Unity 2017.2.0b1.

Notes:
- Reproducible in 2017.3.0a4, 2017.1.0b7, 2017.1.0b1;
- Not reproducible in 2017.2.0a4;
- Reproducible on Windows 10 and OSX 10.12.5;
- Reproducible only for Speedtree shadows, not reproducible for primitive gameobjects (cubes, spheres);
- Reproducible only in Occlusion preview mode; not reproducible in Game view.