Steps to reproduce:
1. Summon a random mob e.g. a zombie.
2. Scale the entity at least tenfold using /attribute command.
3. Try hitting its upper part of the body (above 19 blocks).
4. Notice that your hits don't cause any harm to the creature.

1. Summon another zombie and increase its size with /attribute command, this time at least nine times.
2. Try shooting the top of its head with a bow/crossbow at certain angles.
3. Notice that arrows phase through the creature's chrome dome (head) without harming it in any way.

F3+B shows collision hitboxes, but doesn't portray its "hurtbox" correctly.