I've been having this issue for a long time (On 2 iPads & 2 iPhones). I noticed last time i was in my iTunes account that my password didn't meet the criteria Apple now has for it's passwords (a cap letter + a number). Figured I'd give it a shot. Changed password to meet Apple's criteria, signed in on my iPad and (after a few seconds) all my purchased apps showed up. Not sure if it'll work for others but it worth a shot. Good Luck.