The bug
When a solid entity such as a shulker or boat get levitation, when the player steps on it, they will fall through the uprising entity, through that they will also be pushed aside when falling down.
How to reproduce
This experiment was created with the following command:
/summon minecraft:zombie ~ ~ ~ {Passengers:[{id:"minecraft:shulker",NoAI:1b}],active_effects:[{duration:-1,amplifier:1b,id:"minecraft:levitation"}]}
I've actually tested the command, it worked just fine. Why are you, Neko, changing it (the result is the same except that you get a burning zombie as bonus)?