I think the problem is you don't have the head attached to the body correctly, and you don't have Head and Neck tags set correctly.
First, the head is independent (good), but you need to drag the handle so it overlaps the body and "attaches" to the body. The handle should turn green when this is right. (See the body turns green when the head origin is over the body, linking the head to the body)

Next, I put handles on the torso for "Neck" (I removed your other Neck tags), then I put a handle on the head above the neck. Once I did that slump worked fine.
The above image shows the "Head" handle I put in place. The shot below shows the Neck handle on the torso layer. (You had "Neck" as a part of the head - which is logical, but I don't think is the right way to to it in CH. I have had more luck with the Neck being part of the torso myself - feel free to experiment some more here! There might be more than one way to get it going.)
