The World Federation One Stop Fiqh

Ruling 1414

If after a congregational prayer has commenced a curtain or something similar intervenes between a follower and the imam, or between a follower and another follower who is the link between him and the imam, then the congregational prayer becomes invalid [for the follower who is separated from the congregation] and it is necessary that the follower act according to the duty of one who performs prayers on his own.