I started a plant of this from a cutting that wasn't nearly as robust as that one you showed, Betsy. I think the catalyst to start it growing might be warmth. How warm are you keeping it? Is it getting too cool at night maybe?
At this time of year, our nighttime lows are around 70deg. so if it's not that warm at night where you are, maybe put the pot up on top of the fridge? Heat that baby up and see what happens!
