Succulent issues tend to be slow to show, I suspect issue started a long time ago.

They root easily...place in extremely well-drained mix and anchor..they'll root.

It looks (best I can see) like a stem rot, which probably wouldn't be caused (up there) by watering. But OMG, it should have far more root mass than that...that looks like a new cutting (almost).

The media may well be too peaty and water retentive for a succulent. I haven't grown a jade crassula for some thirty years, but as I remember, you water them well, let them dry for a long time (abusive I know) (sometimes I went a month), then water again.

As a general rule, they thrive on neglect and too much attention is very bad.

That should have sufficient root mass for a six inch pot, but given how little (if any) root remains that would be overpotting probably for now.

Yeah, that would be stem rot. I find my various crassulae plants need far more water than I was led to expect, but it turns out they're thirsty succulents in my heat zone. I water them just before/just as the leaves begin to shivel, which can be as little as twice a month or as often as twice a week, depending on where they are. (The tiny terrarium ones are meant to stay small, so they only get small waterings when they dry out, while my biggest one gets a good drench about monthly.)

With yours, there's no root mass at all but the leaves aren't shriveled, so they're probably pulling moisture from the stems. I would cut off the trunk(s) and root the pieces in a well-draining C&S mix. Once there are a lot of roots, repot into a grit + perlite + C&S blend.

The good news is that there is probably healthy stem tissue above the rot lines, so you've got a good chance of getting a few healthy jade plants out of it.

I would suggest to check whole stem: squeeze gently to feel if it is firm or soft. Soft is most often from overwatering, but sometimes could be from thirst. But don't run to water it, since there is definitely some rot there: 2 spots you indicated are rotting. Cut above, and keep cutting thin slices until there is no dark spots of any shape left in flesh. Leaving any will just cause continued rotting.

You may consider more inorganic mix - while 50/50 mix of C&S soil works for many, more gritty mix will be even better. Using mix of only grit and coarse perlite with just little bit of turface provides great drainage for all my succulents. They spend long time outdoors (as long as my climate allows) and get rained on without any problem. Just a small sample - see the mix they are in: