Insufficient information in your post to answer. Can you provide screenshots of the lineups you submitted?
If you're trying to leverage the "blank the starter and put the player at backup and reserve to get him 48 minutes" approach, there is a hard limit that you can only blank 2 starter positions. If you blank more than 2 starter positions, the coach rejects your submitted lineup as invalid and will generate his own lineup based on the players you set as active/dressed for the game.