Amazon’s cashier-less grocery shop, dubbed Amazon Go by the company, is going through some teething problems, according to the Wall Street Journal.

Specifically, the new shop can’t handle tracking more than about 20 people at the same time, and freaks out “if an item has been moved from its specific spot on the shelf” the paper writes, citing un-named sources.

It’s an ignominious start for what was supposed to be the future of the grocery store. The idea behind Amazon Go is that a highly connected grocery store, with enough cameras tracking every item and visitor, can operate without tills at all. Individuals are authenticated through their smartphones and their movement throughout the shop, and interaction with products, are tracked with a plethora of cameras.

Unfortunately, the shop has had to delay its official opening. Located in Amazon’s home town of Seattle, the store is currently operating in “beta mode” to employees of the company only. But the tests revealed that the shop isn’t quite ready: “For now, the technology functions flawlessly only if there are a small number of customers present, or when their movements are slow,” the Journal reports.

The Amazon Go concept isn’t the company’s only foray into brick-and-mortar retailing. Eighteen months ago, it opened its first physical bookshop, and now plans to expand to up to 400 sites, according to the chief executive of a major shopping mall chain.

Amazon had not replied to a request for comment at the time of publication.