Entities that were summoned while a rotating tp command was running in a repeating command block won't fall down.
How to recreate:
Set a repeating command block running with command like: /tp @e ~ ~ ~ ~10 ~ or /tp @e ~ ~ ~ ~ ~10 (You can use any selector that will target the entity).
Now, use a spawn egg, breed two mobs, drop an item or use the /summon command. the entity will rotate as expected but won't fall.