Unfortunately, this will happen for all blog posts published before moving to the new custom domain.
conversation.js fetches the conversation going on over at the Micro.blog timeline for a specific blog post. In this case, the script is saying, "Hey, give me all replies for the blog post at https://www.stratinator.com/2022/01/23/my-sundayswing-ideas.html".
That URL was never sent to the Micro.blog timeline, and that’s the problem. At the time of posting, the URL was https://microblog.renem.net/2022/01/23/my-sundayswing-ideas.html. Hence the 404 Not Found error.
Unfortunately, conversation.js isn’t equipped to handle the domain move. @manton could probably implement support for it, though. Or, if you are comfortable with theme development, you could mitigate the problem yourself there.