How to reproduce:
1. Download and open the attached project (Google drive link is in the edit)
2. In the Project window double-click on the "DontUseForNow_Sprite HardTint" Asset (found in Assets/Shaders folder)to open the Shader Graph window
3. Close and reopen the project (when the Shader Graph Has Been Modified window pops up press either Save or Discard Changes)

Reproducible with: 2020.2.0b12, 2020.2.3f1
Not reproducible with: 2018.4.31f1, 2019.4.19f1, 2020.1.17f1, 2020.2.0b11
Could not test with: 2021.1.0a1, 2021.1.0b4, 2021.2.0a3 because of the CS0246 error

Notes:
- Opening the project in Unity 2020.2.0b11 or earlier seems to fix the issue and upgrading the project back to a newer version won't reproduce the issue
- Reimporting any script or deleting the "Library" folder fixes the issue
- Removing almost any package resolves the issue as well
- Removing enough Assets will stop the issue from appearing as well