The online retail giant has been accused of poorly policing its platforms before.

In July 2018, two nonprofit groups reported that shoppers could buy onesies for babies stamped with alt-right images, Nazi-themed action figures and anti-Semitic books and music. The groups accused Amazon’s policies banning hateful or offensive merchandise of being “weak and inadequately enforced,” allowing hate groups to “generate revenue, propagate their ideas and grow their movements.”

Weeks later, under pressure from lawmakers, Amazon said it would not let third-party retailers sell products that feature Nazi and white nationalist symbolism on its platform.

Chris McCabe, a former Amazon employee and founder of ecommerceChris, a firm that consults with marketplace sellers, said repeat issues with offensive content partly reflected Amazon’s “reactive” approach to enforcing its policies.

Mr. McCabe said that algorithms trawl the website, looking for items that might violate Amazon policies. Items identified by the algorithm are then typically reviewed by humans who determine whether they should be removed.

The sheer volume of items being sold on Amazon through third-party sellers makes it challenging to identify and remove all offensive items before they are found by the public, Mr. McCabe said. The volume, he added, also makes it impossible for humans to review all items before they are posted. More than half of the products sold on Amazon.com are from third-party sellers.

Mr. McCabe said that the shopping spike during Black Friday and Cyber Monday — the busiest shopping times of the year — would probably stretch Amazon’s enforcement capabilities even further.

“I have no doubt that these weren’t flagged,” he said. “I don’t think it is, for example, a technical error. I think they were flagged. They just weren’t reviewed in a timely manner.”