Reproduction steps:
1. Open project in "StackLitShaderBug.zip"
2. Open "SampleScene" Scene
3. Notice how SSR works on StackLit Material with Shader StackLit Graph CoatSmoothess set to 0

Expected result: when Coat Smoothness is set to 0 Material does not reflect anything
Actual result: Material reflects when its Coat Smoothness is set to 0 and does not reflect when it's set to 1

Reproducible with: HDRP 7.1.5 (2019.3.0b12), 7.1.6 (2019.3.0f1, 2020.1.0a15)
Not Reproducible with HDRP 7.1.2(2019.3.0b12)
Could not test with: HDRP 4.10.0 (2018.4.14f1), HDRP 6.9.2 (2019.2.15f1) because was not able to make StackLit Material reflect anything

Notes:
1. Coat option has to be selected in StackLit Master Settings to make the Coat Smoothness option available in StackLit Master
2. Screen Space Reflection (SSR) has to be enabled in HDRenderPipelineAsset
3. This is a Package regression (first Package regression version HDRP 7.1.5)