Steps to reproduce:

1: Place an "Always Active" "Repeat" command block with the following command:

ride <Name of Player A> mount @e[type=arrow,limit=1]

2: Have Player B shoot an arrow from a bow straight upward at about half charge.

2a: This should make it so that Player A rides the arrow until the arrow lands.

3: Once Player A begins to fall, have Player B shoot another arrow at Player A.

Observed Results:

The second arrow shot by Player B hits Player A, then all three entities (Player A and the two arrows) fall down towards Player B. By Player B's perspective, once the three entities hit Player B, the arrow Player A is not riding falls to the ground, but the arrow Player A is riding continues to bounce off Player B's head, similarly to how an arrow bounces off the head of an Enderman when it can't teleport. (See https://drive.google.com/file/d/1ut-Nv2-EvcrWrd5hrcVldEWNOIFrU9j2/view?usp=drive_link for more.) By Player A's perspective, however, they are just standing next to Player B. In this state, Player A can interact with, break, and place blocks, but only up to the reach limit of how Player B sees Player A. If Player A tries to do anything to blocks outside this range, on Player B's screen, nothing happens. On Player A's screen, however, they see that the block was broken, placed, etc., and then the action was immediately reverted.

Expected Results:

The second arrow shot by Player B hits Player A, then all three entities (Player A and the two arrows) fall down towards Player B, and land on the ground.

Visuals: https://drive.google.com/file/d/1xsjJxMZS7hptAhBtKZMU9SAtnJoMjnM3/view?usp=drive_link