Thanks for the answer Andrew, but I still got questions about this issue.
( Btw, the screenshot is showing movable light shadow, which is a correct case. The problem is shown in the video )
It occurs to the characters without PhysX cloth on their mesh too, so I guess the reason is independent to the subject primitive’s setting.
As the problem never occurs with the movable light, I guess the shadow projection matrices between stationary light and moveble light are different.
Is this the reason? and why should it be?