Got my replacement hub fitted and so far things have been fine running on my H2D. I think this proves that the issue is definitly down to the hall sensor for the hub motor, when replacing the hub the motor is used from the previous hub and is working fine so it must be the sensor that is at fault.
I image that Bambu are fully aware of the issue and we will see a redesign / replacement sensor being used in the near future. I just hope my new hub continues to function without issue, the first one only lasted for just over 400 hours of printing.