404 error on post after posting

Why does this give a 404 error?:

https://fedia.io/m/opendata@lemmy.sdf.org/t/2724091/Why-is-train-data-shared-with-the-Belgian-gov

That was a post that I made to a Lemmy community that was hosted by a server that has been down for over a month. Of course there is no direct access to lemmy.sdf.org, but fedia.io should have its own cached version. It accepted my post, I kept a copy of the link, and now the link is unreachable, even when I am logged in.

I suppose it’s another bug in mbin.