There is a very large scale crawler that uses random valid user agents and a staggeringly large pool of ips. I first noticed it because a lot of traffic was coming from Brazil and "HostRoyale" (asn 203020). They send only a few requests a day from each ip so rate limiting is not useful.

I run a honeypot that generates urls with the source IP so I am pretty confident it is all one bot, in the past 48 hours I have had over 200,000 ips hit the honeypot.

I am pretty sure this is Bytedance, they occasionally hit these tagged honeypot urls with their normal user agent and their usual .sg datacenter.