We got a ZZ plant for my daughter last summer and it has been going well, but recently it has been struggling. We noticed a little leaf yellowing and we thought it might be cramped in the pot (the whole plant was in the small plastic pot shown in the picture). We got a larger pot, repotted it, removed the stalk that was struggling, and moved one stalk to a separate pot because we wanted to have 2 pots anyway. That was three weeks ago and we watered it thoroughly when we spotted it, then again 2 weeks later (the dirt felt dry on top and bottom) as you can see, there is more yellowing. I'm concerned it is the soil - I checked it a week after watering and it felt damp still. I'm concerned maybe I was given bad advise at the plant store to use moisture control indoor potting soil. Not sure what to do now. I could switch soils, but I don't know if that is the cause or if repotting just 3 weeks later would cause to much stress. Any suggestions?
I think the yellowing leaves are a sign of overwatering. You also mention that the soil is still damp after a week, which suggests that the soil has no proper drainage.
You might want to change the soil to new soil with good drainage capacity. That is the opposite of what you use now with the moisture control. What I usually use for houseplants, is to take normal potting soil and mix it with some perlite. This will give the soil good drainage capacity.