I didn’t see anything out of the ordinary in your settings. That behaviour happens when a post does not exist, which shouldn’t be the case.
Could it be that you deleted the topic before the digest was sent out? I have code in place that deletes the digest row for a deleted post, but maybe that never kicked in?
If none of my theories above apply, I’ll need a staging site to continue the investigation. Preferably with SSH access. If your host does not offer SSH access, then SFTP access will do. I’ll need to look at the topic and run some wp-cli commands to try to understand the issue.
I’ve also found room for improvement in the digest code that gets the permalink, so I’ll be applying that as well.