I find ficus to be so dern picky. Since it is dropping leaves one by one, it may be safe to say it is environmental vs too much/too little water, fertizlier etc. Any changes to the environment? More/Less A/C? More cloudy days than normal? Drop in humidity? Raise in humidity? All this can affect a picky ficus. I moved my ficus outdoors as the leaf drop indoors was getting too messy. The change of course made it drop all it's leaves. But it bounced right back in time. They are now over 12 feet tall outside and due for a third trim.