How to reproduce:
1. Open user-submitted project (GradientCustomNode.zip)
2. Open the CustomGradient/CustomGradient.shadergraph
3. Remove the three bottom properties connecting to CustomGradient node and save the graph
4. Without closing the ShaderGraph window import the package, located in the root project folder(CustomGradient.unitypackage)
5. Note that the opened Shader Graph did not update. Closing and reopening the Shader Graph window updates the Shader Graph

Expected result: the ShaderGraph window contents are updated when the shadergraph file is changed while the window is open
Actual result: the ShaderGraph window contents are not updated when the shadergraph file is changed while the window is open

Reproducible with: 2018.4.23f1, 2019.3.14f1
Not reproducible with: 2020.1.0b9, 2020.2.0a11
Could not test with: 2017.4.40f1(package unavailable)

Reproducible with package versions: 7.4.0
Not reproducible with package versions: 8.0.1, 9.0.0 - preview.14