Errors are thrown:
-Retrieving array element that was out of bounds.
-SerializedProperty m_ShaderProperties.Array.data[2].propertyType has disappeared!
-type is not a supported int value.
-Mismatched types in GetValue - return value is junk

Steps to repro:
1. Create a new HDRP template project
2. Windows > Render Pipeline > HD Render Pipeline Compositor.
3. Enable Compositor > Project Window > Assets/Compositor.
4. Open DefaultCompositionGraph > Blackboard > Add Vector1 > Save Asset.
5. Select DefaultCompositionGraph profile > Shader properties > Size > 1.

Actual Result:
Retrieving array & Mismatched types errors in the console.

Expected Result:
No errors in the console.

Reproducible in:
2020.2.0a19, 2020.1.0f1, 2020.1.0b13 with Package version 9.0.0 preview.33.

Note: HDRP Compositor window introduced in 9.0.0 preview.33.

Environment:
Occurring on Windows 10 & Mac 10.15.

Stacktrace:
Retrieving array element that was out of bounds
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)

SerializedProperty m_ShaderProperties.Array.data[2].propertyType has disappeared!
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)

type is not a supported int value
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)

Mismatched types in GetValue - return value is junk
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)