Steps to reproduce:
1. Download and open attached "f4-bugs" project
2. Select "GraphA" in the Project window
3. In the Inspector window press "Open Shader Editor"
4. Select "GraphB" in the Project window
5. In the Inspector window press "Open Shader Editor"
6. In the "GraphB" Shader Graph window select "Sample Texture 2D" node that is in the "New Group" group and press Ctrl+C
7. Open "GraphA" Shader Graph window and press Ctrl+V

Expected result: The node you have copied from "GraphB" gets copied to "GraphA"
Actual result: "InvalidOperationException: Cannot add a node whose group doesn't exist" error appears in the console window

Reproducible with: 2018.4.15f1, 2019.2.18f1, 2019.3.0f5, 2020.1.0a19 ("ShaderGraph" package versions 5.7.2 - 7.1.7)
Could not test with: 2017.4 (No package manager), 2018.4 (Grouping was not available yet)