Ask-a-Dave's-Gardener: Christmas cactus and Christmas tree leaf-like cactus sick?, 2 by eligr8

eligr8 wrote:
Hi,
My Christmas cacti have recurrently been getting this mushy brown look at the base of the leaves. This one that I'm posting pics of already lost loads of leaves and looked like it was thriving with what's left for about 2 months. But now it's suddenly going brown at the base again!
I also have another one that started going the same, but I separated the different plants into 2 pots with new soil and they seem to be on the mend now.
The latest I've noticed is this other cacti with Christmas tree shaped leaves (sorry, I don't know the name) that's also started having what looks like the same problem.
Any tips on what I can do? Could it be some kind of disease that's spreading among my plants?
Thanks!