“It’s sort of chaotic and inconsistent the way that the federal Web has gone down,” said Tom Lee, director of Sunlight Labs, an arm of the open government group Sunlight Foundation.

Lee blamed the inconsistency, in part, on individual agencies making judgment calls based on the White House Office of Management and Budget’s “confusing” shutdown guidance. He said the shutdown has been “very disruptive” for open data groups. He noted, for example, that updates to the Federal Register, which tracks the government’s daily activity, have slowed to a trickle because of the shutdown.

“We’d really like to see, at the very least, clearer guidance in advance about what systems will shut down and how they’ll shut down,” he said.

The administration says there are several explanations for why some websites have been pulled while others remain active. One factor is whether the site operates with annual appropriations or multiyear funding, an OMB official said.