What is the reason for my fiancé's anger and anxiety when performing congregational prayers several times in a row, and is this related to faith or Satan?

We ask Allah Almighty to strengthen faith in your fiancé's heart, to show him the truth as truth and grant him its following, and to show him falsehood as falsehood and grant him its avoidance, and to help him embrace the religion from all its aspects, as He Almighty said: "O you who have believed, enter into Islam completely."

And Allah knows best.