Repro steps:
1. Open new project
2. Add to the project the Terrain Tools package that is checked out to PR revision
3. Open Project Settings
4. Go to the Player section
5. Under "Other Settings" see the Rendering section
6. Uncheck the option to "Auto Graphics API for" your platform. ie Windows
7. In newly appeared reorderable list, click the + button in the bottom right
8. Add one of the following Graphics APIs to the list: OpenGLES3 or Vulkan
9. Drag the newly added Graphics API to the top of the list
10. You will be prompted to reload the project/restart the editor after possibly saving
11. Save if needed and opt to restart the editor
12. Now add a new Terrain to the Scene
13. Select the Terrain
14. Select the Paint Terrain option in the Terrain Inspector
15. In the dropdown for the painting tools, select Sculpt -> Noise
16. Set your brush strength to 1
17. Begin painting on the Terrain

Expected results: There is a visible change in Terrain height when painting noise when older graphics APIs or Vulkan in in use
Actual results: There is little to no visible change in the Terrain height when painting noise when older graphics APIs or Vulkan is in use