Reproduces in Version: 2021.1.0a2.727
Doesn't reproduce in Version: 2019.4

Repro steps:
1. Use a project with universal RP version 10.2.0
2. Create a new shadergraph, create a property on the blackboard
3. Undock the shadergraph tab
4. Redock the shadergraph tab
5. Click the property

If bug doesn't reproduce repeat steps 3 through 5. For me it always reproduced after repeating once.
Expected result: no error
Actual result: UIElements errors will be thrown, which will cascade into more errors and more bugs as more operations are done in Unity, requiring a restart
Note: This is not the only way I have encountered this bug, it's just a reliable way to reproduce it