Is this a problem with OnTriggerEnter?

I posted this question a day ago and had no responses… I've searched for over an hour on google and old unity answers but haven't found the solution so I'm asking again hoping someone else who can help might see it. (I hope that's not against the rules.)

I have a platform that moves down when the player is standing on it, otherwise it moves back up to it's original position.

To do this, I'm using onTriggerEnter to determine when the player is touching a box collider on the surface of the platform. However, when the platform moves down, the motion is jerky. I assume the player is slightly moving off the box collider every frame or so. How can I fix this?

The loop for the elevator is in Update but I tried LateUpdate thinking that might resolve it but it's exactly the same outcome— jerky.