Neiman Marcus shoppers hoping to scoop up Black Friday deals were instead greeted with an error message.
According to Catchpoint Systems, which monitors retailers' Web performance, the luxury brand's homepage has been mostly unavailable since 8 a.m. ET.
It represents the first significant outage of the day, and follows a smooth day of Web performance on Thanksgiving, according to Catchpoint.
Ginger Reeder, a spokeswoman for Neiman Marcus, said the company is looking into the outage.
Catchpoint is monitoring desktop and mobile sites for the top 50 e-commerce retailers from 23 locations across the U.S.
According to its data, Newegg and HP experienced notable slowness with their desktop sites, with Jet.com experiencing slowness on both its desktop and mobile sites.
Problems with Newegg's site escalated during the afternoon, and it was completely down from 11:30 a.m. to 12:15 p.m., according to Catchpoint.
Foot Locker's mobile site also faced intermittent slowdowns or errors, Catchpoint said.
Newegg, HP, Foot Locker and Jet.com did not immediately respond to requests for comment from CNBC.