The Bug

Unlike every other entity, player passengers do not track their mounted vehicle position accordingly when the vehicle in question is being teleported. This issue did not occur in 1.19.4 or prior.

How to reproduce

• Place an active repeating command block with the command below:

execute as @e at @s on passengers on vehicle run tp @s ^ ^ ^1

The issue is more visible when the new position is relatively superior or equal to 1

• Spawn any entity
• Mount an entity with the ride command:

ride @s mount @e[limit=1,sort=nearest,type=!player]