Yeah man, I am having the same issue too. It was working for me last weekend because I got several achievements associated with contracts. This is preventing me from getting the contender achievement at the moment. I also have the PlayStation 3 version of this game and their leaderboards are working. So I am not sure what is going on. Hopefully like you said this is a temporary problem and it’ll come back.
Can confirm that this method works, but very hard to pull off. Was able to pull it off the first round and defeat him, did it again the second time, until my character punches no longer reached him and was defeated. Attempted again but can not manage to pull it off again.