Starbucks Corp. (SBUX.O) investors may be happy this morning, but its loyal app users are less than thrilled with the coffee chain’s digital performance.

The company, which on Thursday reported better-than-expected sales in the U.S., faced criticism on Twitter Friday morning as customers reported problems with its popular smartphone app. The glitches took place the same day Starbucks is giving customers who order a holiday drink a free, limited-edition reusable red cup, likely driving more traffic to both the app and the stores.

“Our sincere apologies. This was not a scheduled maintenance and we are aware of the difficulties customers are experiencing,” Starbucks said on its Twitter account in response to complaints. “We’re working quickly to resolve them.”

Mobile ordering and payment represented 14 per cent of transactions at company-operated Starbucks in the U.S. last quarter.

The company’s shares surged as much as 12 per cent in intraday trading Friday to a record high after it broke out of its home-market slump in its fourth fiscal quarter. The company didn’t immediately respond to a request for comment.