Hi Brian!
Agreed; you said migrated posts are fine so I wouldn’t worry about rebaking or the like. This seems to be an issue with the post-migration configuration.
Are you using an external asset host like S3 or some other object storage API?
Is the site public by any chance, so that we might look at how the posts are rendered?
Failing that, could you paste the raw and cooked fields (inside triple backtick quotes) for a new post that exhibits the issue?