Should the prayer be repeated if the congregants learned that the Imam omitted two letters from Al-Fatiha?

The phrase "they are ignorant of the invalidity of their imam's prayer" means that the prayers of the congregants are valid if they are excused due to their ignorance of the ruling regarding the invalidity of their imam's prayer, and they do not need to repeat it. However, whoever knows of the invalidity of his imam's prayer and continues to follow him, his prayer becomes invalid.