How to reproduce:
1. Open the attached “scriptableobject_issue” project
2. Open the “SampleScene”
3. In the Assets window, select the “testSO” asset
4. In the Inspector, add an element to the “Some Objects” list by selecting the “+” button
5. Save the changes without leaving the Inspector window (CTRL+S)
6. Try adding or removing elements from the “Some Objects” list using the “+” and “-” buttons (or manually typing a number in the input field)
7. Observe the Console

Expected result: The changes are saved, and no exceptions are thrown in the Console
Actual result: NullReferenceExceptions are thrown when the “+” and “-” buttons are clicked. List elements disappear until the Inspector window is refreshed

Reproducible in: 2023.2.0b13, 2023.2.7f1, 2023.3.0a8, 2023.3.0b4
Not reproducible in: 2021.3.34f1, 2022.3.18f1, 2023.2.0b12, 2023.3.0a7

Reproducible on: Windows 10, Windows 11
Not reproducible on: No other environments tested

Notes:

* The first affected version’s behavior differs slightly from the latest versions, but the end result is largely the same
* See attachments for the different exceptions thrown