They are eating way too many grams of carbs so it isn't working. Remember, insulin release makes you hungry. If you cheat, you'll get hungry and then you will probably cheat a little more. Rather than play this stupid game, limit your carbs even further. Some people break a plateau by switching from 3 meals a day to 6 half size meals a day.
Some people break a plateau by cutting all snacks and limiting themselves to three meals a day.
Some people break a plateau by skipping a meal each day. It means you are burning fat. It could be dietary fat. Further, you may be burning ketones and nothing shows up on your ketostix. This is because there is no ketone spillover.