i had this problem the 1st day i hit 50 as well. im pretty sure you can only get 3 wins towards your weekly a day. i was stuck on 3/9, got kind of angry after i won 2 more games and was still 3/9. next day i got a win and it went to 4/9 no problem and then stopped at 6/9. so i guess my advice is to wait till the daily quests reset and see if you can get another win after that.