Errors are thrown:
-Retrieving array element that was out of bounds.
-SerializedProperty customPasses.Array.data[1].passFoldout has disappeared!
-type is not a supported int value.
-NullReferenceException: Object reference not set to an instance of an object

Steps to repro:
1. Create a new HDRP project.
2. Hierarchy > Click on "+" > Volume > Custom Pass.
3. Add DrawRenderersCustomPass & FullScreenCustomPass.
4. Change their name "Test1" & "Test2" respectively.
5. Drag the FullScreenCustomPass to the top of the list.
6. Remove FullScreenCustomPass from the list.

Actual Result:
Errors in the console:
-Retrieving array element that was out of bounds.
-SerializedProperty custom Passes.Array.data[1].passFoldout has disappeared!
-type is not a supported int value.
-NullReferenceException: Object reference not set to an instance of an object

Expected Result:
No errors in the console.

Reproducible in:
2020.2.0b1, 2020.2.0a20 with Package version 10.0.0-preview.27.

Working Fine in:
2020.2.0a20, 2020.1.2f1 with Package version 9.0.0 preview.33.

Environment:
Occurring only on Windows.