Certified GKH Gardening Expert
This can happen for a few reasons. It is best to fertilize at least once per year in spring, as the most typical cause would be a lack of nitrogen. Lack of light can also cause this.
I would recommend fertilizing, and this should take care of the issue. This article will help: https://www.gardeningknowhow.com/ornamental/shrubs/waxflower/chamelaucium-waxflower-care.htm