What is the ruling on one who misses congregational prayer in the mosque due to the imam's mispronunciation (laḥn) in reciting Al-Fatiḥah, and is he obligated to pray in congregation at home with his mother, or is it sufficient for him to pray alone and still be rewarded for congregational prayer if he regrets missing the mosque?

All praise is due to Allah.

Congregational prayer is not a condition for the validity of fasting. No scholar has ever stated this, not even those who consider congregational prayer obligatory. Allah’s justice and generosity are far greater than to nullify a magnificent act of worship like fasting due to a shortcoming in congregational prayer. It is not permissible to compel the mother to pray in congregation with her son, given the great right parents have. The questioner is advised to reflect on the reason for his absence from congregational prayer, as there might be leeway in the matter, and he should adhere to knowledge and moderation. For one who is keen on congregational prayer but is prevented by a legitimate excuse, such as illness, Allah will record for him the full reward of congregational prayer.