Have you trimmed/pruned it at the wrong time?, although they dont really require much pruning from time to time they will need a bit of a trim, or indeed renovation pruning if the plant has got too big, best to carry this out after flowering.

Always trim or prune after flowering, I have pruned mine to a ball shape, it looks very cool. But always after flowering.

Thank you both for your comments. I have regularly pruned the shrub every year after pruning and, apart from not flowering, it looks magnificent. It has always flowered well in the past.