Here is another photo.

Hi, from your picture, this does not look like a succulent to me. It may have started yellowing because it was nutrient deficient, and the yellowing may have continued due to the soil change. If you used a miracle grow product or something similar, it has a lot of nutrients. Maybe it is shocking the plant, especially if the plant was living in a different type of soil and more used to less nutrients for a long time. It may look bad for awhile, lose those leaves and then recover. Keep an eye on it. Also watering once a month seems like it is very little. Be careful that the succulent soil does not make it drain too fast.

How did the roots look when you repotted it?

If it was happy before in that location and in that pot, all you can do is wait it out. Changing the soil may have been quite a big change for it.

It's a ZZ plant, Zamioculas zamiifolia. These plants make tuberous roots that store moisture, so they need some space to enlarge. If the roots have filled the pot, the foliage will start to suffer.

Is the soil dry once per month? Checking for dryness usually works better than a schedule. Sometimes plants use moisture more quickly, so your plant could be suffering times of being too dry, and/or too moist.

Your plant also looks chlorotic (too yellow.) Repotting into fresh soil should help with that also. Try not to pack the soil tightly into the container when repotting, just enough to so plants don't fall out. That leaves some little air spaces in the pot, lessening the risk of rotting the roots (overwatering.) Roots need oxygen and moisture at the same time to function.

After watering, check to make sure water never sits in the drip tray. It's easier for me to take plants to a sink to water so I don't have to try to empty drip saucers in a room with furniture and carpet.