Facebook announced today that over 800,000 users were affected by a bug that unblocked some people that they had blocked on the site. Though it didn't reinstate any friend connections that were severed once a block was put into place, it did open up the ability for an unblocked person to message the user who had blocked them. Facebook said the bug was active between May 29th and June 5th and that around 83 percent of affected users had just one blocked person become unblocked as a result.
Facebook has been dealing with a number of privacy issues surrounding its platform including the Cambridge Analytica scandal and a bug that changed 14 million users' privacy setting defaults to public. Unblocking blocked accounts without a users' consent is a major blunder on Facebook's part and one that could have caused some users harm.
Facebook says it's notifying anyone who was affected by the unblocking error. The bug is now fixed and anyone who was unblocked has been blocked again.