https://forums.autodesk.com/t5/maya-forum/xgen-guide-turn-into-curves-after-rebuild/m-p/9284457#M78731
This solution "half fixed?" the problem. I followed his instruction to turned the utilities off, but the problem remains.
When I looked into my Outliner, there are a lot of empty groups in "xgGroom". I deleted the "xgGroom" group, the problem gone.