Answer: Hibiscus may lose some leaves for a number of reasons, including over or underwatering, warm or cool drafts, reaction to being relocated, and insect problems. Since your plant is growing well, I suspect it may be shading out the lower leaves. These plants tend to be very large and rangy with time, so you will need to prune it back every winter or else trim it back little by little a branch at a time year round. Pruning will delay flowering, so some people prefer the latter method.
In order to maintain that braided effect you will need to snip off the sucker growing at the base or it may overwhelm the braided portion. However, if the leaf problem is severe, you may find that the braided portion has begun to literally choke itself. If this is the case, you might want to cut the braided portions away and grow the sucker as the primary plant instead.
You will also need to repot it, probably also on an annual basis to keep the soil refreshed. Late winter, early spring is a good time to do this.
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