How to reproduce:
0. Set up master or vfx/staging in manifest.json
1. Open the attached project
2. Open VFX asset
3. Create Set Position(Shape:AABox) block in Initialize and convert it to subgraph Block
4. Open created Subgraph and connect AABox operator to Set Position(Shape:AABox) block
5. Expose AABox inline operator and save the subgraph
6. Double click VFX asset
7. --Observe the crash

Reproduced on: 2022.1.0a1(master)

A few lines from the stacktrace:
0x00007ff6d25a2229 (Unity) VFXMemorySerializerBindings::StoreObjectsToByteArray
0x00007ff6d0720946 (Unity) VFXMemorySerializer_CUSTOM_StoreObjectsToByteArray
0x000002a890825885 (Mono JIT Code) (wrapper managed-to-native) UnityEditor.VFX.VFXMemorySerializer:StoreObjectsToByteArray (UnityEngine.ScriptableObject[],UnityEngine.CompressionLevel)
0x000002a890825613 (Mono JIT Code) [VFXGraph.cs:363] UnityEditor.VFX.VFXGraph:Backup ()
0x000002a890825083 (Mono JIT Code) [VFXViewControllerUndo.cs:23] UnityEditor.VFX.UI.VFXGraphUndoStack:.ctor (UnityEditor.VFX.VFXGraph)