Reproduction steps:
1. Create a new HDRP template project
2. Create a new VFX Shader Graph
3. Makes some changes to the graph

Expected result: The Preview Window is correctly showing the current Shader material
Actual result: The Preview Window shows a black node which does not react to the changes made in the Shader Graph

Reproducible with package versions: 7.1.1, 7.1.2

Reproducible with: 2019.3.0b8, 2020.1.0a10
Could not test with: 2017.4.33f1, 2018.4.12f1, 2019.2.10f1(VFX Shader Graph was not available)

Notes:
The VFX Shader Graph feature was introduced in ShaderGraph 7.1.1