Ficus leaf drop
I have a ficus (true rubber plant - is this the benjamin's?). I used to leave it outside from May to October, but it got too heavy and my back too sore, so I brought it in to stay two years ago. It did well, except it was too big - over 6 feet high. I pruned it back pretty hard 2-3 months ago and it seems fine until about a month ago. Since then, it has been dropping leaves like crazy. The leaves are green which, in my experience, means the plant is overwatered. Yet, when I stick my fingers into the soil, it feels dry. I have two meters. Both say the soil is fairly dry on top, and half dry down 8-9". House humidity is around 40%. Light level is low. The plant is in front of a triple window that leads to a back porch. The porch has three outside windows and one small skylight, so the only light is indirect.
The true rubber plant or rubber fig is Ficus elastica (big leaves). Ficus benjamina is "weeping Chinese banyan" (smaller leaves).
With the leaf drop that you describe, I suspect that your plant is Ficus benjamina, because this is a common phenomenon as a response to physiological stress. It could be due to drought stress or other factor.