This is the way I understand this...
Flynn pled guilty. Under oath, he admitted his guilt and agreed to take full responsibility for his actions.
Prior to sentencing, both sides submit their own sentencing recommendations to the court. This prosecution recommendation generally talks about the heinousness of the crimes and the horribleness of the defendant and how they should be severely punished.
The defense recommendation usually talks about the defendants good works and service to his family community country and God, and minimizes the crimes as uncharacteristic lapses in an otherwise saintly life. They recommend a light sentence.
In Flynn’s sentencing memos, among other things his lawyers argued that he should get off easy because the FBI agents tricked Flynn into lying by not being mean enough to him during questioning and .........hey look over there Peter Strzok was one of the agents and he got in trouble for saying mean things about Trump while having an affair. These are Fox News talking points.
Seeing this bullshit in the sentencing memo pissed the judge off. And it seemed to negate Flynn’s under oath admission of total and contrite guilt. Which would mean maybe Flynn was lying under oath then. Which is why the judge wanted him put under oath today. And why the judge was so annoyed.
1. His plea mentioned his full cooperation and acceptance of his guilt.
2. His sentencing memo argued "I only confessed because the FBI cheated".
Both of those things cannot be true. If he was truly guilty & sorry as he originally plead, then he lied when they later filed the sentencing memo and cast doubt on the case. If he was cheated by the FBI, then he lied when he originally plead guilty. Flynn's team was trying to not only mitigate the sentencing, but keep him in good odor with Trump in the hopes of a pardon.