Ashiok has only been attaching nightmares when a card is added to my hand, but not when I play a card.

I used scour the void and not one of the cards I pulled from my opponents graveyard attached a nightmare. This has happened two games in a row now.

I also use refreshment stand as my land card and when I played the card I got from this land it did not attach a nightmare.

I played two games where I only used 50% of potential nightmares.