[Freesurfer] wm surface does not follow wm.mgz

Hi, FreeSurfer experts

I have seen similar posts before but did not think that I could solve the issue based on the answers from the previous posts. So I am posting it here again. Basically, I find that white matter surface does not follow the wm.mgz file (see the attached file). It is strange that such problem is only located at the precentral gyrus. I checked the white matter original surface and the inflated surface and they look fine. I also went through wm.mgz slice by slice to see if there is abrupt gradient between slices and it doe not seem to have that either. So I wonder if anyone would help on solving this issue.

Thanks in advance! Leon