Basically when a player is riding any mob, the mob won't be able to tp correctly.

How to reproduce:

• Summon a camel / horse, tame it and place a saddle.
• Place a command block, set to "repeat" and "always active".
• Ride the camel / horse, WHILE riding paste this command and click "Done" on the command block. /execute as @e[type=minecraft:horse,sort=nearest,limit=1] at @s run tp ~ ~.3 ~

The mob will stay in place instead of tp upwards with the player.