@BryanV how did you point https://discourse-uploads.bokeh.org to your S3 bucket?
I added a CNAME record pointing to the <long id>.cloudfront.net URL for the Cloudfront CDN distribution to our DNS configuration for bokeh.org (which is on Cloudflare in our case, but that should not matter).
For reference, our S3 bucket does not have any dots in the name, but I also don’t recall any specific issues setting up the CDN because of that (or any issues creating the bucket, it just needs any unique name).