Amazon has delayed the launch of its Amazon Go stores due to technical issues that have snagged development of the cashier-less groceries. It turns out, Amazon’s software is having trouble keeping track of people inside the store if there are too many of them, or if they are moving too quickly.

In a test store in Seattle that was only open to Amazon employees, the company’s technology had trouble handling crowds of people larger than 20. The store also had a hard time following an item if it hadn’t been properly replaced in its spot on the shelves by a shopper who may have considered buying it but decided against the purchase. Jason Del Rey writes at Recode:

When I asked Target’s chief information and digital officer about Amazon’s new store of the future in January, he smiled.

“I’m kind of skeptical,” the executive, Mike McNamara, said in an interview at an industry trade show that day.

Just a month earlier, Amazon had unveiled a video touting a new store in Seattle — called Amazon Go — with no cashiers and no checkout lines. In their place, a tech cocktail of cameras and sensors would work together to automatically bill customers on the way out.

But McNamara, who spent 17 years at the British grocer Tesco prior to Target, said the concept had been around for more than a decade.

“It’s 14 years later,” he said, “and we’re still probably 14 years away.”

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