It will have been cached at closer to the edge, but once the TTL expires, so does the cache. That means all the DNS requests that would have been served via loc

It will have been cached at closer to the edge, but once the TTL expires, so does the cache. That means all the DNS requests that would have been served via local caches end up hitting the upstream DNS servers. For a site like Facebook that will be creating an asbolute deluge of requests. Andecdotal but the whole of the internet feels sluggish atm.