Please clear my doubt


Chess.com had made some changes by shifting 10|0 to rapid, so if your blitz rating is higher than your current rapid rating, your rapid rating will be set to your current blitz rating.
I guess, that has resulted in your rating change. Read the full article for more info~
https://www.chess.com/news/view/10-minute-chess-now-rapid-rated-bullet-ratings-increased
Hope that helps.