As part of the upgrades yesterday the DNS record for www.pool.ntp.org
temporarily (and mistakenly, obviously) routed around the Fastly CDN.
For the "real" traffic to the pool system that's totally fine, but there's also a regular background load of HTTP requests from slightly broken/slow clients (mostly in China) that, I am guessing, tries to set the time over HTTP. The new setup is missing a piece to "hold" the slow requests when the CDN isn't active.
There are just a couple cron jobs to be moved before the server migration is complete.