A backup system was deployed for HealthCare.gov on Monday at a lower traffic rate than federal officials projected, signaling there could be further trouble with the system.
The Centers for Medicare and Medicaid Services (CMS) acknowledged that the site's try-again-later system was initiated as roughly 35,000 users tried to access HealthCare.gov at the same time.
Officials said the decision came in response to a slight rise in error rates and response times across the site. CMS spokeswoman Julie Bataille sought to downplay the move, suggesting it was unrelated to the site's overall functionality.
HealthCare.gov is coping with a wave of traffic that is roughly double what the site has seen on a typical Monday, according to the CMS. User interest is expected to go up further this month as people seek to purchase plans that begin Jan. 1.
Reports of the site's functionality were mixed. Some users appeared able to access the system for the first time since it launched on Oct. 1, while others remained bogged down in technical glitches.
The site is facing intense scrutiny now that the Obama administration's self-imposed deadline for fixing the system has passed.
Administration officials claimed victory on Sunday for making the site functional for the vast majority of users, but reports of ongoing problems suggest that there is much more work to do.
One problem that has plagued the system is the flawed 834 forms that transmit applicants' information to insurance companies, creating problems for new policyholders.
CMS said Monday that tech teams had discovered and addressed a single technical glitch that was responsible for roughly 80 percent of the problems with 834s.
"That bug has been fixed and is now working properly," Bataille said. "We have fixed many of the bugs that led to the 834 issue."
The agency did not provide an overall error rate for the forms despite repeated requests.