It's because you aren't taking fall damage when you hit the ground with the elytra open. You take damage from crashing with the elytra, so the mace isn't supposed to cancel the damage out.
This issue started for me after opting into Realms Stories. Is it the same for you?
It's because you aren't taking fall damage when you hit the ground with the elytra open. You take damage from crashing with the elytra, so the mace isn't supposed to cancel the damage out.