Does not reproduce in 7.0.1
Repro steps:
1. Use project with universal RP
2. Create a new shadergraph
3. Create a new subgraph
4. Drag the subgraph into the shadergraph and plug it into the master node (or any other node)
5. Save the shadergraph and close the tab
6. Delete the subgraph
7. Try to open the shadergraph
Expected result: the shadergraph will open with an indicator showing that the subgraph is invalid
Actual result: the shadergraph will not open and errors will print to console