Steps to reproduce:

1. Open the attached project
2. Open 'Canvas Repaint Repro' scene
3. Select the 'TextMeshPro Text' game object in the hierarchy
4. Modify it's font style using the 'Text Mesh pro UGUI' component
5. Notice it does not change immediately, but changes if you somehow interact with the editor after a change (Click anything, drag any window, etc. See this video: https://www.youtube.com/watch?v=ivAY1j0Qff4)
6. If you remove 'Vertical Layout Group' and 'Content Size Fitter' components from 'Button' GO, everything works as expected

Workaround: Force the RepaintAllViews() in the editor mode by adding this piece of code to 'TMPro_UGUI_Private.cs' script:

#if UNITY_EDITOR
UnityEditorInternal.InternalEditorUtility.RepaintAllViews();
#endif