Hybrids are a plant with a genetic quirk, like variegation, that persists throughout the plant's life. Often it can be passed from parent plants. Sports are a plant that has a genetic quirk that does not persist. Plants that are grown from sports (there are quite a few Japanese maples that fit this category but I haven't seen any ficus) must have the vegetation that reverts pruned out regularly.
I do not think your plant is reverting, I think it needs more light. Choose a sunnier window than where it is currently located.