[build buy] new mesh looks distorted

hello! i tried making new mesh for an animated object (private journal ep parenthood) and it has animations in-game and everything but a part of it is distorted.
can someone help me figure out the exact issue and possible fix??

i checked 'animation' in blender and bones are mostly fine, but not identical due to differences in meshes, maybe that's the case?
the issue: drive.google.com/file/d/1TAP-o8rSpnyx7Wq_kYEzzxcuQSmZuDu5/view?usp=sharing
link: broken mod