Where are you located? It is very helpful if you update your profile with the zone you are in or a location. This helps to identify problems that could happen based on the climate in your area.
The smoke bush, if you are in a cold climate, might have gotten hit hard this winter as many folks have had a hard winter. If so, those bare branches may not produce and the plant will just regenerate from the ones growing.
It is still a viable plant and will grow from the new shoot. Hope this is helpful