I would hazard a guess that at some time in the last season your smoke Tree has had an infestation of aphids.
Many of them carry viruses that can cause the effects you are seeing.
Woolly Aphid, Rosy Apple Aphid, and Yellow Bed Straw Aphid can carry things like Reversion virus etc.
Luckily Smoke Trees/bush, can take hard pruning so cut back into clean areas and the plant will be fine. next growing season look out for aphids and treat straight away.
An apple a day.....keeps me in work.