I havn't a prolific knowledge of plant pests or diseases , but looks like an infestation of scale-insect .
A specific insecticide designed to obliterate these horrors might work and save your plant .
Others on the forum might give more specific advice
The overall shrub looks healthy and good, so if it is on some selected branches, I would prune them off. Always thoroughly clean all blades before and afterwards. You can scrub clean the branches if it's quite a small area. But not really ideal on these shrubs, they are a bit delicate. I haven't had success with these shrubs in the past, but it was not due to scale insects.