Did you let them callus before potting? Did you water them? Looks like end of stems rotted or dried up. If just dry, the ends should fall off when completely dry. If rotted, they should be cut off asap until only healthy flesh is left. What kind of soil did you use?

I can't tell if rot or not; rot is usually soft. If dry, they could just snap off. You don't have much stem left. Maybe twist off carefully last pair of leaves and let them root to get couple of extra plants. Let callus remaining stem and pot in dry mix. Don't want to advise you to loose plants, but that's what I would do. But I have too many jades...

If using C&S soil, make sure you add lots of perlite. Ppl that use that mix add min 50%. I use more inorganic mix. But either works well, just make sure they are not wet. Here are bunch of cuttings, they were callusing for a while ('cause I just didn't get to potting them :), then stuck in a gritty mix about 2weeks ago. Didn't water them yet, some are bit wrinkly. But np, as there is plenty of moisture in the leaf for a while yet:

Thanks Rina! BTW your plants are lovely!