Please try to change that line to
comment_form( array( 'fields' => $fields, 'label_submit' => esc_attr__( 'Submit', 'Divi' ), 'title_reply' => '<span>' . esc_attr__( 'Leave a comment', 'Divi' ) . '</span>', 'title_reply_to' => esc_attr__( 'Leave a Reply to %s', 'Divi' ), 'class_submit' => 'submit et_pb_button', 'comment_notes_before'