This particular problem basically boils down to "CDN providers don't like caching large files", which is a very common problem. Everything else was configured a

This particular problem basically boils down to "CDN providers don't like caching large files", which is a very common problem. Everything else was configured and setup exactly right to not have a large bill. Most CDN providers have a lot of machines out on the edges of their networks, and it's understandable that they don't stuff these machines with large disks, likely preferring smaller faster SSDs. But this is a very common pitfall of CDNs that needs more attention, along with messaging on the dashboards and settings pages. I've had problems with no warning on Cloudfront, Cloudflare, Bunny.net all from not realising that my files were beyond the CDN's cache size limit, but none of them seem to do a good job at surfacing this other than "talk to customer support". Cloudfront does list the max size clearly in the limits and quotas page, though, and if you front your S3 bucket with Cloudfront, you could turn caching off and still get the discounted bandwidth out rates (S3 -> Cloudfront is always free, even if the file is fetched every time).