Reproduction steps:
1. Open the attached project.
2. Open the 'testScene'.
3. Select 'Main Camera' game object and uncheck 'Allow MSAA' checkbox.
4. Play the scene.
5. Check the Console.

Actual behavior:
- Got the color: (0,0,0,0)

Reproduced with:
- Metal

Not reproducible with:
- DirectX

Note:
- Cannot test with OpenGL ('Platform does not support compute shaders' error message)

Solution:
Set Camera targetTexture.