I had just recently repotted my Ruby Glow after noticing it was 4 different plants. I potted them in a slightly bigger pot, and they were all thriving and doing really well. One day, I looked and saw one was looking sad. I touched the stem and it instantly came out of the dirt black and rotting.
It was never over-watered, and in fact is often under-watered. There are no signs of bugs or the like. Eventually another one of the plants just died.