When Teleporting Players using either Manual Commands or Command Block Commands, if they Jump after the teleport is completed they will die from Fall Damage.

It seems that it is considering the Distance Traveled as a Fall Damage factor causing them to Die.
The Death Message even says "Fell to their Death"

EDIT
I discovered that this Teleporting Death only occurs if the Teleport Destination is Up or Down from the location of the player (Higher or Lower Y Coordinate from the Player)