How to reproduce:
1. Open the attached project named "Case_1242459"
2. Open Test Scene
3. Enter Play mode
4. Select the Sun gameObject
5. Click "Switch Light Intensity"
6. Observe the change in lighting
7. Disable Rotation Update
8. Observe the Scene lighting again

Expected result: Ambient lighting is updated at step 6 and there is no change in scene lighting at step 8
Actual result: Ambient lighting is only updated when the rotation of the directional light is stoped

Reproducible with: 2019.3.12f1, 2020.1.0b8, 2020.2.0a10
Not reproducible with: 2018.4.22f1, 2019.3.0f2

Reproducible with package versions: 7.1.7, 8.1.0
Not reproducible with package versions: 7.0.1, 7.1.5
Could not test package versions: 7.1.6