To repro:
- download party.zip project
- open it with 2020.2.5f1
- set rendering API to DeirectX12, i it's not already
- build and run

Expected Result: build finishes with no errors
Actual result: there ae erros thrown and the build fails

Reproducible in 2020.2.5f1, 2021.1.7f1
Regressed version: 2020.2.5f1
Not reproducible on 2020.2.4f1 or earlier, trunk(2021.2.0a5)
Not reproducible when attempting to build with Directx11, or Vulkan

When switching bac to DirectX12, after building for DX11, the build no longer gives any errors

Shader compiler: Compile Particles/Standard Surface - FORWARD, Vertex Program: Internal error communicating with the shader compiler process. Please report a bug including this shader and the editor log
Shader error in 'Particles/Standard Surface': Internal error communicating with the shader compiler process. Please report a bug including this shader and the editor log.