(Bloomberg)—Starbucks Corp., the world’s biggest coffee-shop chain, suffered crashes at some of its payment systems following a routine technology update.

The problems struck cafes in North America, preventing an unspecified number of registers from working, according to company spokesman Reggie Borges. Starbucks is No. 462 in the newly released Internet Retailer 2017 Top 500.

“We were doing a technology update for our store registers in the U.S. and Canada, and a limited number of those locations remain offline,” he said. “Stores are still open. Customers are still able to get their orders.”

The glitch hit at a time when Starbucks’ payment technology is facing more scrutiny. Its mobile-ordering systems have caused congestion at pickup counters, irking customers and weighing on sales. In some ways, the technology is a victim of its own success. Starbucks’ smartphone app has become increasingly popular: At some of its busiest U.S. locations, the mobile order-and-pay system handles at least 20% of transactions.

Last month, Starbucks reported quarterly sales that missed analysts’ estimates, giving investors more reason to worry about technology hiccups. It now falls to CEO Kevin Johnson, a tech-industry veteran who just took the helm last month, to fix operations and reignite sales.

The technology update that caused the outages took place early Tuesday morning, Borges said. “When it was time to get them back up, some of them didn’t take,” he said.