Reproduces in:
Version 2019.4.28f1 (1381962e9d08)
Version: 2020.3.13f1.629
Version: 2021.1.8f1.2516
Version: 2021.2.0b1.3029
Version: 2022.1.0a1.191

Reproduces with Shader Graph package versions 7.x.x, 10.x.x, 11.x.x, 12.x.x

Repro steps:
1. Create 2 subgraphs, Rec1 and Rec2
2. drag Rec2 into Rec1 and save it
3. Backup Rec1 using the file explorer (copy it into another folder) (don't copy the meta file) (bug only repros if you copy it into a folder INSIDE your assets folder)
4. Delete the Rec2 node in Rec1 and save it
5. Drag the Rec1 subgraph into Rec2 and save Rec2
6. In the file explorer, replace Rec1 with the backup (overwrite it)
7. Go back to unity

Expected result: the subgraphs update and show errors because of the recursion
Actual results:
In 2019.4, the project will crash refuse to open upon restarting
in 2020.3, Unity hangs, requiring it to be closed using the task manager. Upon restarting, the project will not open, with an error message (see MovingFileFailed.png) (might not happen consistently)
in 2021.1, 2021.2, and 2022.1, Unity hangs, requiring it to be closed using the task manager. Upon restarting, the subgraphs will behave as expected, with errors.