Thanks for your work on this, @cquest! Here are a couple of things I noticed.
In the United Kingdom category, I see this post titled Welcome! which I don’t see on the old forums United Kingdom category. It looks like it corresponds to this post which is in the old forums Sweden category. However, this migrated post in Discourse also includes a bunch of replies that aren’t present on the old forum post. I’m not sure if this is a one off issue or indicative of something bigger, but it seems worth investigating.
In each category I’m also seeing what looks like an automatically generated post named About the {Category Name} category with some boilerplate text. These posts are not present in the old forum categories. Like this one for example.