Nordstrom Inc.’s e-commerce checkout page on its website and app had a brief issue July 12 that prevented shoppers from placing an order.

The site was never down and issue is now resolved, a spokeswoman for the retailer says.

The issue occurred during Nordstrom’s anniversary sale.  On July 12 1.67 million consumers visited Nordstrom.com, which is more than a 50% increase in traffic from just the day before when 1.11 million consumers visited Nordstrom.com, according to SimilarWeb data.

To apologize for the inconvenience and “the issues” consumers may have experienced, the retailer emailed Nordstrom credit or debit cardholders and offered 10 loyalty points per dollar for purchases that took place during the interruption.

Nordstrom did not comment about what caused the checkout issue. Bob Buffone, chief technology officer at web performance vendor Yottaa, believes the issue was likely a caching problem on the anniversary sale day’s landing pages.

The “first byte” time on Nordstrom.com’s homepage was more than 0.75 seconds, which is extremely long and indicates a poorly cached site, Buffone says. The first byte time is the time it takes for a shopper to see any content at all.

“If those pages were better optimized for caching, the site would have been able to better handle the huge surge of traffic they experienced during their promotion,” Buffone says. “Caching of dynamic content when traffic bursts is essential to scaling the infrastructure.”