I've played hundreds of hands of Blackjack but the achievement for playing 10 hands hasn't unlocked. The achievements for 10 spins of Roulette and 10 goes at the slots unlocked as normal but Double Down is still locked.

I don't know if it makes a difference, but I played my first 10 hands of Blackjack at the Atomic Wrangler, before playing any other game. I got the other two achievements later while playing at Gomorrah. I've been kicked out of 4/5 casinos (just The Tops left) and played 10+ hands of Blackjack in each. No dice - literally and figuratively.