Facebook users are reporting one of the stranger bugs to plague the platform of late: years-old Messenger threads resurfacing automatically, without context or explanation. First reported by users on Twitter, the company now confirms that older messages are being treated as new, unread ones and popping up in the Messenger tab on Facebook.com.

“Some people are seeing older messages on Facebook.com. We are aware of the issue and are actively working to resolve it in as soon as possible,” a Facebook spokesperson tells The Verge. “We apologize for the inconvenience.”

Some have expressed concern that the bug could resurface conversations or past histories they would much rather forget. Unless you actively delete the history between you and another user, Messenger retains the entirety of your back-and-forth conversations, stretching back years. It could be jarring to some to be hit with an old thread with an ex or a family member or friend who has passed.

This isn’t the first time something like this has happened by accident. Back in 2015, Facebook notoriously began resurfacing painful memories for people using its On This Day callback feature. That’s because the underlying algorithm didn’t seem to know how to differentiate between the celebratory, cheerful posts it was designed to resurface and those about tragedy that often generate as much, if not more, “engagement,” as Facebook measures it.

Although this time, it looks more like an issue with code rather than a strategic failure of human understanding. And, to be fair, the vast majority of people complaining about the bug just seem to be treating it as a random and quizzical oddity of the social network that nobody can explain right now. Yet knowing that others are being haunted by painful memories is a good reminder that Facebook is responsible for a vast amount of online identifies and the details of our personal lives, and its stewardship of that data has come under near constant criticism this year.

Later on in the evening, Facebook said it had resolved the issue, which it attributes to software updates. “Earlier today, some people may have experienced Facebook resending older messages. The issue, caused by software updates, has been fully resolved. We’re sorry for any inconvenience,” a Facebook spokesperson said in a statement to The Verge.

Update 11/27, 1:05AM ET: Added second statement from Facebook confirming it resolved the issue.