Singapore could be due to being a common VPN exit node for within SE Asia? Close by and avoids the most common regional blacklists (and gov firewalls of course).
I saw lots of Singapore traffic back in the early 2010s too, and often see it listed on random free VPN and proxy sites
I think it's due to Tencent Cloud providing cheap servers in Singapore. I had the same issue and blocked all of their offending IP ranges from these ASNs and it was all Tencent or Huawei Cloud.