Praying in congregation in the mosque is obligatory for men who are able to do so, according to the more correct scholarly opinion, because of evidence that has been discussed previously in the answers to questions no. 8918 and 120
Recitation of al-Faatihah is one of the pillars or essential part of the prayer for the imam, the one who is praying behind the imam and the one who is praying on his own. This has been discussed previously in the answer to question no. 10995
Reciting al-Faatihah is not waived for the one who is praying behind the imam except in two cases:
(i) If he catches up with the imam as he is bowing. In this case he should bow with him and the rakah will count for him, even if he did not recite al-Faatihah
(ii) If he joins the imam in the prayer just before he bows (rukoo) and he is not able to complete al-Faatihah. In this case he should bow with him and not complete al-Faatihah, and the rakah will count for him.
You should try hard with the people at the mosque to advise the imam to slow down in his prayer and not rush. If the imam bows before you have completed al-Faatihah, it is permissible to you to complete it even if that will make you delay bowing, then you can follow him. But you should recite al-Faatihah more quickly, without taking your time. Some people are not able to recite al-Faatihah behind the imam for that reason.
Shaykh Ibn Uthaymeen (may Allah have mercy on him) was asked: What is the ruling on a man who offers a four-rakah prayer with a congregation from the beginning of the prayer, then when the imam says the salaam, this man stands up and does a fifth rakah. When the imam asked him about that he said: In the second rakah I was not able to recite al-Faatihah so I did this rakah to make up for it?
He replied: This is correct, but what would have been better than that is if, when he stood up and the imam bowed before he was able to complete al-Faatihah, he had completed al-Faatihah and followed the imam, even if the imam had already stood up from bowing.
End quote from Majmoo Fataawa Ibn Uthaymeen, 13/134
We do not think you should stop attending the mosque or repeat the prayer; rather you should pray with the imam so long as his prayer is correct, and try hard to do what you are obliged to do, even if you fall behind in following him, whilst continuing to advise him in a suitable manner.
And Allah knows best.
Reproduced from Islam QA