[Issue raised on the forums: https://forum.unity.com/threads/cant-open-graph-due-to-compile-error.823749/#post-5590510]

Repro steps:
1. Import the attached package.
2. Open New VFX
3. Drag the FrequencyRangeParticle subgraph in the VFX
4. Observe console errors:

Note:
- Opening the Subgraph first triggers a slot resync after which the issue no longer reproduces:
Slots have been resynced in Empty Subgraph Operator of type UnityEditor.VFX.VFXSubgraphOperator
UnityEditor.VFX.UI.VFXViewWindow:LoadResource (UnityEditor.VFX.VisualEffectResource,UnityEngine.VFX.VisualEffect)
VisualEffectAssetEditor:OnOpenVFX (int,int) (at Library/PackageCache/com.unity.visualeffectgraph@7.1.7/Editor/Inspector/VFXAssetEditor.cs:169)
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)