The sense of calm that has pervaded the US stock market for months is masking unprecedented bursts of volatility in individual shares, say Barclays Plc strategists. Last year was a case in point, when some of the biggest components in the S&P 500 Index saw abnormal swings as the gauge registered an AI-led, 16% rally. Between the 100 largest index members, there were 47 instances of sharp selloffs — specifically, a drop of five standard deviations or more, a move so rare it’s often considered an anomaly, a ...