From further into Teukka’s thread:

u/ramenporn on Reddit r/sysadmin speculates that an erroneous BGP config change was pushed this morning, which locked out anyone who wasn’t physically local to Facebook’s BGP core routers:https://t.co/VAg979Ijsx pic.twitter.com/AKAnrQtago

— Jim Salter (@jrssnet) October 4, 2021