It's not unusual for any of the many species of Ficus to defoliate as a result of any one or more cultural issues known to be stressful to the plant. How quickly the plant bounces back from the indignities heaped on it, or whether it even CAN, often depends on whether or not the plant has enough reserve energy to push a new flush of foliage, and how skillful the grower is at identifying and correcting/eliminating the conditions that caused the stress/strain in the first place.

Pay particular attention to soil choice, light levels, temperature, and nutrition. If you can keep those influences in the 'very favorable' zone, your plant should respond in kind.

Many growers habitually provide one to several cultural influences at the periphery of what the plant is genetically programmed to tolerate and expect the plant to grow as though everything was being provided at luxury levels. Things don't work that way. It's up to the grower to learn how to provide conditions that ensure no limitations, because it's always the least favorable cultural influence that limits growth and vitality.

Getting your soil choice right so you can water and fertilize correctly is extremely important, and likely to make more difference to your successes than any other single factor.

Al

A lot of ficus will do that with a sudden change. They seem to reach an equilibrium under certain conditions, as in being kept fairly dry, and then sudden availability of lot of water makes them lose leaves. New leaves follow soon and the plant settles into an equilibrium again under the new conditions. I get that happen in moves from very wet to dry and vice versa. Your plant should come good, just don't "drown" it with too much water. They often start off life as an epiphyte, meaning water runs off immediately, and they have air around the roots.