Retail robots that can scan shelves and update inventory have been one of the most visible faces of automation in recent years, but the success of such machines is far from guaranteed. As first reported by The Wall Street Journal, Walmart — one of the biggest adopters of this technology — is ending a contract that saw shelf-scanning robots appear in some 500 of its stores. The retailer found that humans could do the job just as well.

Walmart began using robots supplied by Bossa Nova Robotics in 2017, with initial deployments in 50 locations. The mobile robots would simplify routine work in stores, said the company, using machine vision to scan shelves and identify what products needed restocking. Earlier this year, Bossa Nova said it planned to expand to 1,000 Walmart stores.

Why exactly Walmart is ending the partnership is unclear, though it seems the global pandemic had an effect. The WSJ reports that as more people began shopping online, Walmart found it had “more workers walking the aisles frequently to collect online orders.” It seems that these workers could then perform the same inventory checks as the robots. Additionally, the WSJ says that Walmart’s US chief executive John Furner had worries about what customers would think seeing robots in the company’s stores.

A spokesperson for Walmart confirmed the news to The Verge, saying: “We’ve worked with Bossa Nova for five years and together we learned a lot about how technology can assist associates, make jobs easier and provide a better customer experience. This was one idea we tried in roughly 500 stores just as we are trying other ideas in additional stores. We will continue testing new technologies and investing in our own processes and apps to best understand and track our inventory and help move products to our shelves as quickly as we can.”

According to the WSJ, the end of the contract has had a big effect on Bossa Nova, with the startup since laying off 50 percent of its staff. Sarjoun Skaff, Bossa Nova’s co-founder, told The Verge in a press statement that the company had been forced to “streamline” its operations as a result of the COVID-19 outbreak, but offered no comment on the contract with Walmart.

“I cannot comment on Walmart, however, the pandemic has forced us to streamline our operations and focus on our core technologies,” said Skaff. “We have made stunning advances in AI and robotics. Our retail AI is the industry’s best and works as well on robots as with fixed cameras, and our hardware, autonomy and operations excelled in more than 500 of the world’s most challenging stores. With the board’s full support, we continue deploying this technology with our partners in retail and in other fields.”

Update November 5th, 4:20AM ET: Story updated with confirmation from both Walmart and Bossa Nova.