When I first bought my Desert Rose from Walmart there was a part of the caudex that seemd brownish and a tad soft, but the rest of the plant is okay. So I continued to purchase it. I have it in a low container and in full sun in my garden and if I do water I avoid wetting that brownish side, and just go watering on the root area below. So far it has managed to bloom and is growing well. But the brownish mark stayed, seems more like a bad skin problem now for my Desert Rose.
I don't know if you can see it in this photo, on the right side there is that patch of brown on the plant, but the rest is gray green.
I am thinking it may have gotten the brown patch due to incorrect watering during shipment and sale, causing that patch to show but later on dried out, so it did not proceed to eventual rotting. So maybe you need to see how the water splashes on your plant during watering. And make sure it does dry out well later.
