VX-1 Li-ion no power by key on after strange behavior

Hello yesterday we had strange behavior on one VX-1 Li-ion scooter.

(1) Rider twisted grip to acceleration side -> Vehicle accelerated (normal behavior)
  -> Rider twisted back grip to regen side -> Vehicle once decelerated (normal behavior) but soon after accelerated (abnormal behavior)
      -> Rider killed power supply by key-off -> Vehicle stopped
(2) After (1), We cannot supply power to vehicle by key-on.
(There is not any reaction on Instrument Panel.)

could you help me to understand what happened and How to solve it?