Physics asset issue - some Body parts Shaking, Head bone detached

Like title says, Here’s a picture of default body : https://s1.postimg.org/1i4k2w1djz/phat-default.png

If Picture is not enough you can check the asset file : https://www.dropbox.com/s/p86vpbhy5w…cs.uasset?dl=0

And here’s a picture of physics simulation : https://s1.postimg.org/6xsldoah1r/phat-headissue.png

as you can see head bone seems not connected to the Body like the rest of the bones, also some of the bones are jumping like crazy, I don’t know which ones are responsible of this, And I don’t know how can I attach the Head bone like the rest are, any idea what’s wrong with it ? Thanks.