Apparently, it was a misconfigured file which screwed up name servers for many or all of the facebook urls. A nameserver converts, e.g. the “user friendly url google.com” to the “actual address” 142.250.72.46. It’s a humongous database. Name servers talk to each other and since Facebook’s name server is authoritative for FB URLs, the misconfiguration was propagated to pretty much the whole world. Once they figured it out, they had to send it out to, eventually, all those servers. It took a few hours to find and fix and several more to propagate the fix.
Apparently, it was a misconfigured file which screwed up name servers for many or all of the facebook urls. A nameserver converts, e.g. the “user friendly url google.com” to the “actual address” 142.250.72.46. It’s a humongous database. Name servers talk to each other and since Facebook’s name server is authoritative for FB URLs, the misconfiguration was propagated to pretty much the whole world. Once they figured it out, they had to send it out to, eventually, all those servers. It took a few hours to find and fix and several more to propagate the fix.