Reproduction steps:
1. Create the project with any template
2. Import the “BugRepro” package
3. Open the “Assets/Test/Test.unity” Scene
4. Select the GameObject in the Hierarchy window
5. Righ-click on the Test component in the Inspector window and click LogTexturePropertyNameIDs
6. Observe the Console window and see that
Variant: 0
Instantiated Variant: 0
Flattened Instantiated Variant: 9
7. Click to open the “Assets/Test/New Material Variant.mat” material in the Inspector window
8. Repeat the 4-5 steps
9. Observe the Console window

Expected result:
{{Variant: 9}}
{{Instantiated Variant: 9}}
{{Flattened Instantiated Variant: 9}}
Actual result:
{{Variant: 9}}
{{Instantiated Variant: 0}}
{{Flattened Instantiated Variant: 9}}

Reproducible with: 2022.3.51f1, 6000.0.24f1, 6000.1.0a2
Couldn't test with: 2021.3.44f1 (Could not resolve compilation errors)

Reproducible on: Windows 11
Not reproducible on: No other environment tested