Reproduction steps:
1. Open the attached “BugRepro” project
2. Open the “Assets/Scenes/SampleScene.unity” Scene
3. Enter the Play Mode
4. Observe the Game view

Expected result: All characters ("長押し : トルネード") are rendered in the same style
Actual result: "ネ" character is greyed out

Reproducible with: 6000.0.58f1, 6000.2.3f1, 6000.3.0b1

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

Note: Selecting the "TMP SubMeshUI [font_system SDF - OutlineBlue + font_system SDF Atlas 1]" GameObject in the Hierarchy window and clicking on the “Face” panel under the material component in the Inspector window refreshes the material and fixes the issue temporarily