Reproduction steps:
1. Open the attached “repro_IN-72668“ project
2. Open the “/Assets/Scenes/SampleScene.unity“
3. Open either the Scene view or Game view
4. Observe the “Sphere“ GameObject

Expected result: The “Sphere“ GameObject appears red
Actual result: The “Sphere“ GameObject doesn’t appear red

Reproducible with: 2021.3.37f1, 2022.3.23f1, 2023.2.17f1, 6000.0.0b14

Reproducible on: Windows 10 (22H2)
Not reproducible on: No other environments tested

Notes:

• Reproducible in Player
• The custom surface shader defines a pass that should render the “Sphere“ GameObject red, or, in other words, return a (1,0,0) value. However, the Editor is also drawing the fallback shader's "Diffuse" pass after the custom shader's pass. This fallback shader pass most likely defines a different color, overriding the red color definition
• Frame Debugger shows that the “Diffuse“ shader’s pass is drawn after the correct surface shader’s pass. This confirms that both the fallback shader and the custom shader is invoked