I messaged JBS too, they said the fluctuating boost im getting is probably due to the actuator closely governing the boost. Seems the turbo wants to just go and go. I'm still none the wiser whether my boost fluctuation is the throttle opening and closing or the actuator clumsily controlling the boost.
My tuner said it held boost steady on the RR and didn't notice it on his test drive (he wouldn't have as you need a good stretch on open road where you can be flat out).
Maybe similar to yours looking all good but on the road not so.
I've still got the standard exhaust, I'd like to rule that out as a issue and I still think a hybrid turbo is I overkill.