You say when your players get bad ratings your team lose matches. But i guess is the opposite. When you lose matches, your players get bad ratings.

There is not anything you can do to avoid bad ratings. It is random. You put players with high morale, high healthy and high win bonuses and...maybe your players get low ratings.

And because one player get bad ratings on one match, he wont get bad rating again on next match.

Stats are like in real life. Only stats. Not useful. Only info.