WHy do the xenons on my 06 plate vrs sometimes reallign (go down then up) and sometimes not when i turn them on?

they will only do this once immediately after the engine has started. You should hear the zssh zsh noise, but will only see it if the lights are on and its dark when it happens.

Level sensor(s) or maybe a motor sticking?

As gadgetman says they do it when you start the car regardless of whether the lights are actually on or not. If the lights aren't on you won't see it happening.