Falling yellow Fiddle fig leaves

Overwatering fig trees will cause them to drop their leaves. Underwatering might too, but it would mostly be bottom leaves.

Try to check out the roots to see if they look nice and healthy.

It's possible to give too much water while not watering too often. If the soil has not dried out in 7-10 days, you are giving too much water and waiting another 10 days and keeping that schedule is not the answer. IF this is the case, water more frequently with smaller amounts.