How to reproduce:
1. Open the attached '1291952.zip' project
2. In the Project window double-click on the 'Blank' Shader Graph
3. In the Shader Graph window reconnect the edge between the Out(1) port of the Float node and the Alpha(1) port of the Alpha node

Expected result: The edge connects to the Alpha node, no visible errors present
Actual result: The Alpha node gets deleted, multiple errors appear in the Console

Reproducible with: Shader Graph 9.0.0-preview.14 (2020.1.14f1, 2021.1.0a6),10.1.0 (2020.2.0b11, 2021.1.0a6)
Cannot test with: Shader Graph 8.2.0 (the Blank Shader Graph is not introduced), 9.0.0-preview.14 (2018.4.29f1, 2019.4.15f1, 2020.2.0b11), 10.1.0 (2018.4.29f1, 2019.4.15f1, 2020.1.14f1) (the Shader Graph package versions are not supported)

Notes:
- The following errors are thrown in the Console:
InvalidOperationException: Cannot remove a node that doesn't exist.
InvalidOperationException: Sequence contains no matching element
InvalidOperationException: Sequence contains no matching element
- After reproducing the issue other nodes can not be created or deleted. The Graph begins to shift in the Shader Graph window
- After trying to add a new node 'ArgumentNullException: Value cannot be null' appears in the Console