Plants can lose leaves and they may also turn yellow or wilt due to overwatering. You could try checking the roots (for root rot)by gently sliding the plant out of the pot, if the roots look brown, mushy or have a sour odor, it could be root rot. Be very careful about letting the plant sit in a saucer with any water in it. If it is not in an active growing stage it may not need as much water. I would not water it if it is wet a few inches down. It probably doesnt need fertilizer until spring.
If all is well with the watering, check the leaves for spider mites, tiny dots underneath the leaves that may also leave some white webbing (this could also cause yellowing). If they are present you will have to treat the plant for them. Increasing humidity around the plant also helps get rid/prevent mites.
One other factor is: it could need more light, even though it is near a window the light is naturally dimmer in the winter months. Since edulis is a tropical plant it may be shedding leaves due to a decrease in light. It may be beneficial if you could add a grow light for it.
Some people are successful with rooting cuttings in the winter. I recently rooted some sunburst cuttings but had trouble with others. Maybe someone else has more info on rooting the edulis and will comment:)
You will have to do some investigation to see what the exact cause is but these are my guesses. I hope it helps. GL
~SJN