ACI Worldwide Inc (ACIW) shares plummeted 8.46% during intraday trading on Thursday, a sharp decline that puzzled investors as the company reported strong second-quarter results and raised its full-year guidance just before the market open.

The payments technology company reported Q2 revenue of $430.4 million, a 7% year-over-year increase, but it slightly missed the consensus estimate of $430.6 million. However, adjusted earnings per share of $0.54 easily beat the analyst estimate of $0.29, and adjusted EBITDA of $91 million also exceeded expectations. The company raised its full-year 2026 revenue guidance to a range of $1.895 billion to $1.925 billion and adjusted EBITDA guidance to $545 million to $560 million.

Despite the overall positive earnings report, the stock's decline may be attributed to several factors. The slight revenue miss, coupled with misses on operating income and pretax profit versus estimates, could have raised concerns about profitability. Additionally, a 25% drop in net new annual recurring revenue bookings to $18 million, caused by the timing of expected Payment Software contracts, and pressure in the Biller segment where revenue net of interchange fees fell 3%, may have dampened investor sentiment. The stock had also been trading at a higher valuation multiple compared to three months ago, potentially leaving it vulnerable to profit-taking after the earnings release.