it looks like mechanical damage-something brushing against it,even a cat and certainly a dog could do it. or, perhaps, wind, it can flex and tear leaves and cause leaf drop.

If the stems are turning black and soft/mushy, then it's rot (possibly from over watering).

Thanks for the replies!! I suppose the leaf breakage is quite possibly thanks to my 2 dogs that do run around quite a lot..i sure hope it's not because of a pest of some sort. Also, i have been watering a little more frequently the last week as it is fairly hot here, hope the roots aren't too rotted beyond repair though. Thank you davez7anv and ewwmayo for the help!

How good is the soil drainage? If it drains very fast you should be able to water freely. If it is draining poorly, you'll need to address that.

Much kudos goes to Rina for the detailed response with helpful photos!

Sans, I've been using standard black compost soil for my kalanchoes for about 3 weeks now and haven't had much problem..though I have read that using a cacti/succulent potting mix is more ideal, so might just switch over soon..

Rina the stem was a little soft and the leaves connected to that stem were beginning to turn black too but yes there is a little leaf sprouting from the dead stem! Looks like it might not be completely dead yet. I have not tried to propagate my plants yet but am eager to try especially after looking at how well yours turned out!! Lovely pictures!!

Thanks everyone, I only began getting into gardening a few weeks ago so am really a newbie at this, really appreciate all the help!!