Hi and
to the forum.
I suspect that the Nominal battery voltage setting in the controller is set to a lower voltage than the battery's nominal voltage.
If the throttle was activated when the power was turned off, the voltage in the controller's capacitors would quickly drop below the Overvoltage protection value, causing the motor to briefly jerk.
If your controller is set to a nominal battery voltage of 24V and you are using a 36V battery, the battery voltage may be too high to allow the controller to work as the fully charged battery voltage
(42~43.8V) would be higher than the 36V Overvoltage protection value.
Or, if your controller is set to a nominal battery voltage of 36V and you are using a 48V battery, the fully charged battery voltage
(54.6~58.8V) would be higher than the 52V Overvoltage protection value:
What voltage Magic Pie did you purchase, and what is the nominal voltage of the battery you are using?
If you have the correct USB programming lead and PC software
(or the Bluetooth dongle and smart phone App if it's a MP5) you should be able to set the controller's Nominal battery voltage setting to the correct value to match your nominal battery voltage.
Alan