Currently the image links for the backside of the cards are broken, so when you generate a deck it wont stack properly. To fix this save the deck generator object by right click > save object, then go to
Documents > My Games > Tabletop Simulator > Saves> Saved Objects > Deck Builder.json

open it in some text editor, ctrl f "backfaceurl" and replace the fabdb2 link with an image of whatever card back you want. Save that and then place the object down from saved objects and you'll have it properly generating your deck!