How to reproduce:
1. Open the attached project
2. Open scene TestAB
3. In the Hierarchy window, select the GameObject "Canvas"
4. Enable the GameObject by enabling the checkbox at the top of the Inspector window
5. Press the Play button
6. When in Play mode and focused in the Game view, press D

Expected result: no exceptions are thrown
Actual result: an exception is thrown: "NullReferenceException: <...> TestLoad.LoadImageUnity (System.Int32 index) (at Assets/TestLoad.cs:54)"

Reproducible with: 2020.3.25f1, 2021.1.0a4
Not reproducible with: 2021.1.0a5, 2021.2.6f1, 2022.1.0b2
Could not test with: 2019.4.34f1 (The AssetBundle 'topbar' can't be loaded because it was not built with the right version or build target. UnityEngine.AssetBundle:LoadFromFile (string)