This question pointed out that there are still a number of links to posts on the old Astronomy SE site kicking around, and that they mostly redirect to new, unrelated questions and answers in the new Astronomy site. I feel those links should have been automatically edited at the time of the migration, but it doesn't really matter, since a quick query turns up ~30 or so sites, which can easily be edited manually.
I do find one thing pretty weird, though: when those links are posted as a raw URL, they still format correctly, for some reason. As an example, see this question, which until recently contained the explicit URL
This feels weirdly buggy to me, though of course the real bug is that the URLs were not auto-updated to begin with.