Ebike wiring?

I have a 750W bafang midrive with 48V 12ah Panasonic battery, No wires for lights so I tapped into hot wire from battery to headlight (48V or 36V LED) the is an aux. white wire from the headlight so I run that wire to power source (motor) and also tee off the white wire before the power source to a knock down transformer to 12V to run tail lights (12V LED), I charged battery to full and drove bike until fully discharged and it worked wonderfully, then I charged battery to full again but now at half charge the motor will start stop start stop until I charge battery to full again then at half charge it starts stops starts stops.

The distributor showed me picture of a motor that has separate wire for lights (6V) and they think it is my lights causing the problem but that is a little confusing to me because it all worked before? I wonder if the knock down transformer sends back voltage and confuses the controller???

Anyone have any idea??? Would installing diodes help??? Thank You...