How to reproduce:
1. Open attached project
2. Add Vector 2 to blackboard
3. Add Vector 3 to blackboard
4. Hold Undo/Redo these changes
5. Observe console

Expected result: change are undo/redo-ed and not errors appear in console

Errors:
Exception while setting value for slot o of type UnityEditor.VFX.VFXSlot: UnityEngine.MissingReferenceException: The object of type 'VFXSlot' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
at (wrapper managed-to-native) UnityEngine.Object.get_hideFlags(UnityEngine.Object)
at UnityEditor.VFX.VFXGraph.OnInvalidate (UnityEditor.VFX.VFXModel model, UnityEditor.VFX.VFXModel+InvalidationCause cause) [0x00082] in /Users/justasz/Documents/test/New Unity Project (11)hd/Library/PackageCache/com.unity.visualeffectgraph@13.1.0/Editor/Models/VFXGraph.cs:654
at UnityEditor.VFX.VFXModel.Invalidate (UnityEditor.VFX.VFXModel model, UnityEditor.VFX.VFXModel+InvalidationCause cause) [0x00000] in /Users/justasz/Documents/test/New Unity Project (11)hd/Library/PackageCache/com.unity.visualeffectgraph@13.1.0/Editor/Models/VFXModel.cs:403

Also error thrown 2022.1:
Assertion failed on expression: '!AssetDatabase::IsAssetDatabaseInitialized() || !AssetDatabase::IsAssetImporting()'
UnityEditor.EditorApplication:Internal_CallUpdateFunctions ()

Reproduced with: 2022.1.0a13 (13.1.0), 2021.2.0b17 (12.1.0)
Does not reproduce with: 2022.1.0a12 (13.0.0), 2021.2.b15 (12.0.0)