It’s not just you — Facebook seemingly logged out everyone’s iPhone on Friday night.
Facebook isn’t down, but it did start an odd trending topic on Twitter Friday night as confused iPhone owners tried to figure out why the social network logged them out. I haven’t found an explanation for why this happened, but it appears that everyone accessing the app via an iOS app has to log back in, and many people who use SMS two-factor authentication were initially having trouble reconnecting.
Based on social media posts, many of the people with two-factor authentication enabled were eventually able to log back in, but the SMS codes were very slow to send, and some have had to upload pictures of their ID to regain access.
https://www.engadget.com/facebook-iphone-outage-logout-061740231.html