Thank you very much for your reply! I checked my server’s score status and found that my server is handling 10.104 out of every million requests. According to this post (https://community.ntppool.org/t/adding-servers-to-the-china-zone/88), this means my server processes 100 requests per second, but in reality, it could be much higher, to the point where my service provider considers it a DDoS attack:(
I believe this is indeed related to the insufficient number of volunteer servers in the China region. I am trying to contact the administrators to address this issue.
Thank you very much!