Reproduction steps:
1. Open the attached project named Case_1187359
2. Open the "Test" ShaderGraph file
3. Add a Multiply Node just below the Blackboard
4. Disable the Blackboard
5. Observe that the Blackboard is invisible
6. Disable the Node preview for the Multiply Node

Expected result: The Blackboard and its sliders remain invisible
Actual result: The Blackboard's sliders become visible

Reproducible with: 2019.2.0a1, 2019.2.7f2, 2019.3.0b5, 2020.1.0a7
Not reproducible with: 2017.4.32f1, 2018.4.10f1, 2019.1.14f1

Reproducible with package versions: 6.5.2, 6.9.1, 7.1.2
Not reproducible with package versions: 4.1.0, 5.16.1

Notes:
1. ShaderGraph 6.5.2 became available in 2019.2.0a1
2. The node must have its preview window disabled for the issue to occur(Track_1187359_V1)