A number of Facebook posts from the period around the Jan. 6 insurrection went missing from the social media service.
The posts -- which covered anything from personal updates to violent incitement -- disappeared from the Crowdtangle transparency tool that Facebook uses to allow researchers to track what users are saying on the platform, reported Politico.
"If Facebook knew about this, and just didn't tell anyone, I think researchers should be pretty concerned about that fact," said Laura Edelson, a New York University academic who was part of the team, which included researchers from Université Grenoble Alpes, that discovered the missing data.
The lost posts have been unavailable since at least May, and the company told Politico they were accidentally removed due to a data limit on its technical transparency tools but the error had been fixed.
Lawmakers asked the social media giant Friday to turn over internal documents and data linked to the U.S. Capitol riots, including information about how election misinformation spread on the site.
The academics who found the problem believe that tens of thousands of posts from the days before and after the riots were still missing, but Facebook said all the original posts were available directly through the site, and a spokesperson said about 80 percent of the posts flagged by researchers should not have been available on Crowdtangle because they had been deleted or made private.
"Researchers do assume that they are getting all the public content from Facebook pages that are indexed by Crowdtangle," said Edelson, whose account was suspended last month for her separate work around political ads. "Those assumptions have been violated in this case."
Facebook is currently dismantling its Crowdtangle team after the tool was repeatedly used to trace how extremist content and misinformation spread across that site and the company-owned Instagram platform, and the tech company was forced to release statistics that showed COVID-19 misinformation was still some of the most popular content on the platform.