Repro:

1. Open the attached ArrayInspectorTest project in 2019.4.
2. Open Samples/SampleScene.
3. Select GameObject and in the inspector, fold out "Other Actions"
4. Set array size to 2, click "" button on first action and click "Add Binding".
5. Observe inspector and note that binding displays properly.
6. Click the "" button again and select "Add Positive/Negative Binding".
7. Toggle the foldout on the newly created binding back and forth.
8. Observe inspector and observe that the foldout correctly adjusts the height of the inspector.

9. Close the project without saving the scene.
10. Open the project in 2020.3+.
11. Click the "" to add an item to the same list as before.
12. Click the "" button on the element and select "Add Binding" in the menu that pops up.
13. Observer the scrollbar that appears and that the item is not visible.
14. Click the "+" button on the element again and select "Add Positive/Negative Binding".
15. Observe that now that bindings appear correctly.
16. Toggle the foldout on the newly added binding multiple times. Note how the height of the inspector adjusts incorrectly.

Seems to come down to PropertyDrawer.GetPropertyHeight() being called during Layout rather than Repaint and TreeView not yet having updated its own layout when its totalHeight is queried.