From your description, it could be 'Rhododendron (leafhopper' (Graphocephala fennahi)
They are small and hard to spot due to their green and red pencil-like stripes.
They can also stop the plant from flowering due to a fungal desease which they carry, which kills the flower buds.
A difficult bug to control, as they fly about from bush to bush.
Eggs are layed in the buds which turn grey-brown.
I would recommend removing any dead or infected buds and destroying them, you should be able to do this by twisting and pulling with your fingers.