What is the reason for the confusion and stuttering when leading friends in congregational prayer, despite mastering recitation and tajwid when praying alone?

This confusion during Imamate arises from the fear of error and an excessive concern with not making mistakes. The remedy for this is to increase self-confidence and reliance on Allah, and to be mindful of His greatness and to be sincere towards Him. Therefore, do not pay attention to what people think, but rather attach your heart to Allah alone, knowing that He is the Giver of reward and punishment, and that people possess neither harm nor benefit.