Inconsistent soil moisture
Ficus like to have consistently moist soil, so be sure to not over or underwater your Ficus. Be sure that your watering schedule is consistent–water when the top inch of the soil is dry.
If you accidentally let your ficus tree’s soil dry out completely, you may need to soak the tree’s container in the sink or tub to properly rehydrate the soil. Keep in mind that when the soil goes from bone-dry to saturated, it can cause stress for your Ficus and cause leaves to drop.
Not enough humidity
Ficus will thrive in slightly humid environments. Increase the humidity around your plant by misting the leaves on a regular basis, using a pebble tray, or moving a humidifier nearby.
Was the plant just moved, shipped or otherwise shocked?
Generally, houseplants don’t like change. They can be cranky for a few days or even a few weeks after they arrive at your home, or after a move to a new location within your home. Give your plant some time and it will likely recover by itself if all other care requirements are being met.
Most of all, be patient!
Let nature take its course – if you’re seeing new growth, keep doing what you’re doing!