They're "galls" caused by (unsurprisingly) gall insects. There are a number of different species of insect that lay eggs in the leaves and the plant causes a swelling around them. The eggs hatch and the larvae feed on the plant. They're relatively common but some plants are more susceptible to them than others. It looks like that species is prone to them. Plants get by okay but look like the 'proverbial'. Picking off the leaves and burning them reduces but doesn't stop the problem. There's plenty more where those came from. If you're prepared to use chemicals there are systemic insecticides, they go into the plant and poison the insects that are feeding on it. Another option is to search for another species of Lillypilly that is not favoured by gall insects.