Sorry about the delayed response. So SVG's were a security venerability so we removed them from the imgix CDN and the were moved to the amazon server to be served as a document. They are the only image format served like this.
Originally on the Amazon server they weren't run through the CDN. They should be now, so if you have some older images not coming through the CDN try removing and re-adding them to make sure they're delivered form the correct doman.
All images, except for SVG's, should be coming from images.prismic.io
SVG's should be coming from <repo-name>.cdn.prismic.io/<repo-name>
(if they are coming from prismic-io.s3.amazonaws.com/<repo-name> then remove and re-add them to deliver them from<repo-name>.cdn.prismic.io/<repo-name>)