This appears to be the same behavior I experienced after enabling the CDN in the yml:
https://meta.discourse.org/t/using-object-storage-for-uploads-s3-clones/148916/211
I’m not sure I understand the described fix though.
Regarding the rebake failure, there really isn’t much I’ve configured beyond the CDN and S3 for uploads and backups. I’ve tried starting from scratch and I experience the same rebake failure after enabling the CDN.