I was doing the tavern brawl today (Only basic, common and rare cards allowed build a deck) and had a demon hunter deck and I discovered with Jumpscare! a demon and also shuffled into my deck a Vengeful Walloper and it had the dark gift Summons a 2/2 copy when played and when I drew and played it it did not summon a 2/2 copy.
Yeah this exact thing happened to me, in arena
Discovered 6/6 rush with copy off jumpscare, drew it later, the copy didnt summon