Ragdoll - Part of mesh left behind

I have created a ragdoll using a model I created in Blender, that I sub in for the character when they are killed. I have managed to get the ragdoll to fall over properly and not totally spaz out, but I have found that the character's crotch region remains frozen in space when the ragdoll is created.

I have other rig based animations on the character from the same model so I'm pretty confident that the bones are properly deforming the mesh. See images below:

So far so good...

But after death, the model's crotch remains frozen:

One thing to note is I added a face to the mesh in Blender to his crotch (there were some wonky vertices there when I originally created the model. However, I added this face after adding the Armature. So I'm not certain if this is more of a blender problem.

Also, this ragdoll is essentially the default created through the wizard.

Any tips are appreciated, thanks!