Hi there.
This seems to me like one frame off error.
If the child actor is the driver and it is the only thing jittering it might be because of the tick order. Sometimes driver ticks before the forklift.
Can you try moving the driver’s tick post physics and say if it has any meaningful difference?
If that doesn’t work, please try to update the child actor’s position in the tick of the forklift manually and see if that works.