The resolution came from contacting the host. This site has an external DNS, so I did not expect this issue, but a CNAME record added in the host DNS for the subdomain of the feed caused it to resolve.
We have other sites where the blog subdomain is setup in external DNS only and it works, so I don’t know why it happened this way, but a good thing to keep in mind.
I hope this helps someone else in the future!
