Network ownership problem

My game has transport, physics, which is completely controlled by the server. each BasePart of the car is set as SetNetworkOwner(nil). the player can sit in a Seat (not a vehicle seat). everything is fine until any accessory is attached to the player while he is in the Seat. after that, once every 3 seconds, for some reason, the server momentarily gives the physics of the car to the player, which causes a lag. exactly once every 3 seconds

how to prohibit the server from giving physics to clients?