I have a similar problem to another use and have posted a picture of it here. My crassula 'calico kitten' plant was super healthy but a few months ago started dying from the inside out. It looks like the inner part of it is just drying up. The hanging branches still look healthy, but I noticed today the healthy-looking branches are indeed snapping off and breaking because of the issues on the inside.

The timing of this coincided with several factors, which could be contributing:
-moved to a new home with less light (now mostly east facing light)
-winter in boston and placement next to a cold window
-i transplanted ~1-2 months before it started looking sick

Any ideas of what I can do to save it? What type of soil does this plant need?