Try testing the soil moisture near the bottom of the pot, rather than just on the surface of the soil. If the soil underneath is too damp, the roots will probably start to rot. Try also moving it an area where it gets more light, and set up a small fan to blow gently over it, to help evaporate extra soil moisture. Here's useful information: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm
I would take it out of the pot and check the roots for rot. All the roots and stems should be firm and whitish. Look for anything that is black and smelly, if this is found, I would take cuttings which lay out to dry for a couple days, then pot up in a cactus soil mix. Each individual round leaf will also start a plant if it is further gone.
Leave this plant dry out thoroughly between watering and make sure it has great drainage.
Thanks for asking your question!