So the leaves are turning dark and drying or moist. Could be from the repotting, but I think moisture issue.

The soil in the photo looks as if it could use more porous material in it.

Better that the soil dries back relatively quickly and evenly through out.

Rick

I agree with Rick--I experienced this blackening myself--excessive moisture. Stratifying the media would be okay when growing plants
in the ground, but for container-grown plants…I don’t know think so.

For sure, leaf appearance is a good indicator of problems
that are occurring or had occurred. I
had this one adenium that I up-potted, and a few weeks later noticed the leaves
were turning dark. On close inspection,
I found that the plant was rotting—so I cut off the caudex and roots at the
apex, applied rooting powder, and planted it.
There was too much moisture and one of the plant's roots was damaged during the up-potting. This is an example of my experience of “problems that are occurring.”

An example of “problems that had occurred”: My plants didn’t get water for 3 days and they were quite dry; I had
held off watering because it seems every time I water, rain comes within a few
hours. And so, it finally rained, and
two days after the rain, I noticed that many of my plants had yellow leaves and
were falling off. My observation is this:
By the 3rd day, as a survival mechanism, the plant cut off water supply
to the leaves to prevent water from transpiring. So even after a good drenching, the leaves
were already dying and destined to drop. This had happened once before, so I know for sure the underlying cause for the yellow leaves--lack of moisture.

-Kadie