It took a second to figure out what was happening.
The TLDR is that the page in question doesn’t provide the necessary metadata in its source (it seems to be added after load), which causes the error in Ghost.
Unfortunately, this is a Substack thing, based on how they generate this page, and can’t be fixed until those elements are included. It is weird that it only affects some pages and not all.
A workaround is to use one of the individual posts from this author. They seem to work perfectly fine.