Weird model clipping problem when customizing metahuman character

Hi! I customized a metahuman character with metahuman creator, and tested it on official expression animation, some weird model clipping problems happened. But if I used the preset character, everything was perfect. Why does this problem occur? Is it metahuman’s bug or internal design limitation? And how can I get rid of this problem by following certain guidance? Thanks for any help!

Custom Metahuman Character:

Preset Metahuman Character:

Another question: I can scale character’s head, but when I export the model, head’s size doesn’t change at all:(