It’s wise to set a low TTL for your A records if you are not 120% certain that your server will be absolutely reliable, and that’s why I leave them at 300 seconds all the time in case of emergencies. The caching server’s network was (and still is) under DDoS, resulting in wide fluctuations in speed and latency. (Does this sound familiar? :/)
I’ve switched to the origin server and turned on Cloudflare for now. Expect slower speeds in China.
I’ll continue to monitor the situation and keep this post updated.