How to reproduce:
1. Create a new project which uses Forward rendering with 1 pixel light allowed
2. Add directional light to the scene (sunlight)
3. Import the attached "case_1050091-AlderTree_problematic.unitypackage" package, and drop "Alder_LOD" prefab in a scene
4. Rotate and move your camera around (an example is shown in the attached video "2018-06-21 11-54-31.mp4")

Expected result: Shadow on the tree does not flicker in and out when rotating the camera
Actual result: Shadow on the tree flickers in and out, depending on some arbitrary camera positions and/or angle

Reproducible with: 2017.1.4p2, 2017.2.3p1, 2017.4.6f1, 2018.1.6f1, 2018.2.0b10, 2018.3.0a3

Note: Changing the shader's render queue seems to have an effect on the problem but cannot resolve it completely. Problem is most visible on LOD transitions, as well as shadow cascade transitions.