Amazon.com Inc.’s web outage left some users unable to access the online retailer’s site for about 20 minutes Thursday, but the disruption had little, if any, impact on Amazon Marketplace sellers.

“Amazon definitely had a front-end outage—as best we can tell it was very intermittent and short-lived. The back-end, which is how our servers and sellers interact with Amazon, didn’t seem to suffer any type of outage or interruption,” says Scot Wingo, executive chairman of ChannelAdvisor Corp., whose online marketing services include helping retailer clients sell goods on web shopping portals like Amazon, eBay Inc. and 50 others in the United States and abroad.

“I’m sure there were some lost sales (for Amazon Marketplace retailers), but I doubt it was material,” Wingo said Friday. About 140 retailers in Internet Retailer’s 2015 Top 1000 Guide use services from ChannelAdvisor. Retailers that ChannelAdvisor added in Q4 include Birchbox Inc., No. 255 in the Internet Retailer 2015 Top 500 Guide, and Indochino Apparel Inc.

Internet Retailer estimates 20 minutes of downtime cost Amazon (No. 1) about $3.75 million in missed sales.

Amazon.com experienced a service disruption at 2:19 p.m. Eastern on Thursday, according to DownDetector.com, a site based in the Netherlands that collects status reports and disruptions on websites. DownDetector.com logged more than 13,000 reports about Amazon during the outage, with 43% reporting issues with the website, 35% with login and 17% with checkout, the company says.

Amazon has not commented on the outage and issued no notifications via its Twitter accounts or website. Users on Thursday received an error message stating “We’re sorry! An error occurred when we tried to process your request.”