Steps to repro:

1. Open Unity 5.5.0 on Windows;
2. Extract attached package and open 'test' scene;
3. In the Hierarchy double click on 'Main Camera' gameobject;
4. Drag the camera on z-axis until you see tree billboard in the GameView;
5. Drag the camera on the opposite direction until LOD0 - green tree is displayed;
6. Repeat steps 4 and 5 2-3 times;
7. Observe the GameView.

Actual result:
At some point of LOD transition (usually LOD3-LOD2 or LOD2-LOD1) shadowy artifacts appears in the GameView on terrain's surface (see attached gif video).

Regression introduced in Unity 5.5.

This could be D3D specific error.

Notes:
- Reproducible in 5.5.0a3;
- Not reproducible in 5.4.0f1, 5.4.0b25;
- Reproducible only on Windows 10 in DX 11 (checked);
- Not reproducible on OSX 10.11.5 in GlCore;
- Reproducible only in the Editor's GameView; not reproducible in SceneView;
- Not reproducible in Standalone build.