Received a quick response from Fazua :-
"Thank you for your e-mail and your interest in our e-bike motor system.
As you describe it i assume as well too low cadence as the root cause.
As the optimal support depends on the cadence and torque. Hereby we demand from our drivers a round kick and constant pedal pressure,
just to get the optimal support from our system. Should an irregular kick or not even pedal pressure take place, in exceptional cases, it may be that the system feels that it is losing performance or support."
It seems down to low cadence and not having a smooth pedal stroke! Have arranged to take to dealer to have software checked,