Julie Bataille, a spokeswoman for the Centers for Medicare & Medicaid Services, said at a separate CMS press briefing that visitor traffic has been about twice as high as the level of traffic HealthCare.gov has been averaging on Mondays from midnight to noon.

HealthCare.gov managers activated a site feature called a "queue," or "waiting room system," when they found that heavy traffic was starting to hurt site performance, Bataille said. The system requires excess users to wait before using HealthCare.gov plan research and enrollment tools, to protect the performance of those tools.

CMS officials have said that the enrollment system should now be able to handle 50,000 users at the same time.

On Monday, however, system managers found they needed to activate the waiting room system when user volume was somewhere between 30,000 and 40,000, Bataille said.

Also during the CMS press briefing, Bataille said:

• CMS has determined that one bug involving handling of Social Security numbers has been causing about 80 percent of the reported problems with issuance of the so-called "834" plan enrollment completion messages. Bataille was unable to say how many 834 message problems site users have actually experienced.
• CMS will cope with the lack of a complete back-office system for administering Patient Protection and Affordable Care Act (PPACA) exchange plan premium subsidies by temporarily using an existing Medicare system to administer the payments.
• At least one insurer -- Blue Cross and Blue Shield of Florida -- is expanding a new pilot program that lets insurers calculate subsidies for consumers and enroll consumers who are eligible for the subsidies directly, rather than forcing the consumers to enroll through HealthCare.gov. CMS officials said Sunday that 16 insurers in three states are participating in the direct-enrollment pilot program.