Reproduction steps:
1. Open the attached project named "Case_1154051"
2. Open the CutoutWithoutSlider shader with shader graph
3. Observe the preview window, notice that the sphere has cutouts
4. Delete the Vector 1 node attached to AlphaClipTreshold

Expected result: Shader does not change as the AlphaClipTreshold value remains the same (0.5) after the node is deleted
Actual result: The cutouts disappear even though the value is the same as before (0.5)

Reproducible with:2018.4.1f1, 2019.1.3f1, 2019.2.0b3, 2019.3.0a3
Could not test with: 2017.4 ( Lack of a Package manager )

Tested package versions: 4.1.0, 4.10.0, 5.1.0, 5.13.0, 6.5.3