Since it hasn't been mentioned, my first thought is valid users browsing on iOS with iCloud Private Relay enabled.

https://support.apple.com/en-us/102602

I have this enabled on my iPhone and websites that report my IP show the block is owned by Cloudflare or Akamai.

Found the list! It might be worth checking if your suspect traffic is from any of these subnets: https://mask-api.icloud.com/egress-ip-ranges.csv