This is a known issue that we don’t have a good solution for yet.
The CDN we currently use – and every other CDN we’ve tried – is slowed significantly by the Chinese Firewall. We have no plans to invest in infrastructure inside China, so we recommend using a VPN or proxy like Shadowsocks. As you’ve seen, sites are much more responsive thus.
Last week was an important meeting of the Chinese Communist Party on 26–29 October, and the filtering is particularly aggressive during those. That makes the performance even worse.
Things appear to be returning to “normal” (i.e. bad but not horrible) this week.