The bug
Passengers get off mobs if they convert into other mobs. The opposite also happens.
How to reproduce
Enter a command in overworld:
/summon ravager ~ ~1 ~ {Passengers:[{id:piglin_brute}]}
You will notice that in the end, piglin brute will get off the ravager when it turns into a zombified version.
Or enter this command in overworld:
/summon hoglin ~ ~1 ~ {Passengers:[{id:villager}]}
Then the hoglin turned into a zoglin will expel villager from the passenger seat.
Linked issues
is duplicated by
Comments

Interesting, for piglins and piglin brutes this was fixed