It is probably not due to your players. It is from the program itself. I called it as 'players being blocked from performing as they should'. You will feel as if the players don't want to play, don't want to score or act like players 3-4 stars below their displayed quality. There could be something regulating the percentage efficiency of the players, where sometimes, for whatever reason(s), the percentage efficiency of many of the players in one team is set to a significantly lower value. Another thing that I have noticed in this game is the injection of poor form to many players of a team so that this team has a significant disadvantage for whatever reasons. This effect may last for quit a while. Many things appear to be 'constructed' in this game so that it follows whatever has been decided by the program.
During such 'bad' periods, there is nothing much you can do. You can try to grind out narrow wins, draws and avoid big defeats by selecting appropriate tactics. The only way to override such bad effects is to have a team that is way too superior in quality than the opponent, for example having an 8-9 star team for playing against a 4-5 star team, where all the disadvantages set to your side will be not enough to cause your team to lose or draw. But, I don't recommend doing it; this game is not worth putting so much time, effort and money.