Reproduction steps:

1. Open the attached “Repro“ project
2. Open the “Assets/MaterialVariantBug/MaterialVariantBug.unity“ Scene
3. Select the “Assets/MaterialVariantBug/MirrorRed.mat“ Material
4. Change the “Smoothness” value to “0.5” in the Inspector
5. Select the “Assets/MaterialVariantBug/Mirror.mat“ Material
6. Lock the “Smoothness” value by right-clicking on it and selecting “Lock in children“ in Inspector
7. Observe the spheres in the Game View
8. Change the “Smoothness” value to “1” in the Inspector
9. Observe the spheres in the Game View

Expected result: Both spheres reflect the new smoothness value of the Mirror Material
Actual result: Only the blue sphere follows the smoothness of the Mirror Material

Reproducible with: 2022.3.17f1, 2023.2.4f1, 2023.3.0b1
Couldn’t test with: 2021.3.34f1 (Required functionality isn’t present)

Reproducible on: M1 MacOS 14.2
Not reproducible on: No other environment tested