While no specific date was released, Richard Thames Rowan, UNO Program Manager said:

"The UNO development team is aware of the problem that some people are having with matchmaking and has a fix going through certification right now. Hopefully, you’ll see this roll out soon, so no need to email anyone."

I know personally I've had this issue and it's great that it's being fixed, now maybe I can get those last two achievements. :)

You can check out the entire post on K1lla's Xbox Domain.