Locked down shoppers have taken less than a week to snap up all Naked Wines Plc’s U.K. Christmas offers, crashing the retailer’s website in the process. Naked Wines is No. 169 in the Digital Commerce 360 Europe 500.

Promotional packs containing items such as bottles of wine and olive oil sold out in about three to four days, according to chief financial officer and U.K. managing director James Crawford. In a normal year, this would have taken two or three weeks, he said. Such was the demand, the Naked Wines website went down for about 40 minutes on Nov. 12.

“People are expecting to be buying online,” Crawford said in an interview after Naked Wines reported first-half results and increased its forecast of full-year sales growth. “They know that it’s going to be challenging because of courier and warehouse capacity and all of that stuff. And actually, they’re making sure that they get their order in early.”

Ecommerce sites crashing during the Cyber 5 period (Thanksgiving through Cyber Monday) or during a large sale is not unheard of. While this crash occurred before a peak period, Naked Wines was likely experiencing elevated traffic from consumers stocking up for their Thanksgiving meals, says Bob Buffone, chief technology officer at performance optimization vendor Yottaa. Looking at the site, Buffone says it could have crashed with the elevated traffic for a number of reasons, such as the site using two content delivery networks and because it was self-hosted.

Last year, Buffone says Yottaa identified about 50 brands that had significant problems that led to angry shoppers and lost revenue over the Cyber 5 period.

“We anticipate that with higher traffic volume this year there will be even more outages,” Buffone says. Already, website traffic is up about 20% year over year for the 1,500 clients that use Yottaa’s performance software, he says. 

“Many retail brands are on ecommerce platforms, such as Salesforce Commerce Cloud or Shopify, which is good in terms of maintaining basic site performance,” he says. “However, the third party technologies that brands add to their sites, such as live chat, personalization, and customer reviews, are external to the platform and any one of these can cause a site outage during peak periods—or at any time for that matter.”

Besides optimizing the site, identifying potential third-party technology issues and load testing the site for increased traffic, Buffone recommends for merchants to established an emergency plan for site performance issues before Cyber 5.

More than half of Top 1000 Digital Commerce 360 retail sites achieve 100% site availability, with the average site availability being 97.3%, according to Digital Commerce 360 analysis of Blue Triangle website performance data. That average means there’s still a lot of room for improvement, as retailers cannot risk their site being down for even a moment as they could lose out on critical sales.

Every minute of downtime can cost companies an average of $5,600 per minute and anywhere from $140,000 to $540,000 per hour depending on the size of the company, according to research firm Gartner. Naked Wines did not respond to a request for comment.