On the former, I don’t think I have access to run that, as my Discourse is hosted by y’all, or at least I don’t know how I would.
On the latter - I’m not sure I follow you. My embedding config is:
which should match the URLs of both the old site and the new site, surely? Apart from the post-specific slug at the end, the URLs of the posts which fail to load the comment topic are identical to those of the posts which succeed in doing so?