Reproduction steps:
1. Create a new HDRP template project
2. Create an HDRP Lit Shader Graph
3. Change the color of the material to illustrate the issue more clearly
4. Set the material type to Subsurface Scattering

Expected result: The preview window is accurately showing the current shader material
Actual result: The material in the preview window appears completely black

Reproducible with: 2019.2.10f1, 2019.3.0b8, 2020.1.0a10
Not reproducible: 2018.4.12f1
Could not test with: 2017.4.33f1(HDRP was not available)

Not reproducible with package versions: 4.1.0, 6.7.1
Reproducible with package versions: 6.9.0, 7.1.2

Notes:
Saving the shader and then resetting the material type to Subsurface Scattering seems to fix the issue