Champions of the Perfect doesn't return the beheld card to hand

[Lunafreliana]

[[Champions of the Perfect]] were destroyed and then exiled due to the [[Darkness Crystal]] but the card I beheld with Champions of the Perfect was never returned to my hand.

[github-actions]

Champions of the Perfect - (Gatherer) (Scryfall) (EDHREC)

{3}{G}
Creature — Elf Warrior
6/6
As an additional cost to cast this spell, behold an Elf and exile it. (Exile an Elf you control or an Elf card from your hand.)
Whenever you cast a creature spell, draw a card.
When this creature leaves the battlefield, return the exiled card to its owner's hand.

The Darkness Crystal - (Gatherer) (Scryfall) (EDHREC)

{2}{B}{B}
Legendary Artifact
Black spells you cast cost {1} less to cast.
If a nontoken creature an opponent controls would die, instead exile it and you gain 2 life.
{4}{B}{B}, {T}: Put target creature card exiled with The Darkness Crystal onto the battlefield tapped under your control with two additional +1/+1 counters on it.