The rating system changed today. Sadly they decided to make the change as hidden as possible. Everyone had their past contests recalculated and currently everyone has 2 different ratings. The public one (Code Chef rating) and an hidden one (the new Elo-MMR rating).
Since today, only your Elo-MMR rating will update. And since this is a different rating, it is very likely it was different than your old rating. Your public rating will converge to the Elo-MMR rating within a few contests.
In the near future, everyone’s old rating will be set to the Elo-MMR rating. Why it was not done already I don’t know.