I am hesitant to say that I have good news or that I have fixed anything...
I honestly don't know if there is anyone left still using this site after all the problems we've had.
That said, I noticed that there were some very recent (as in yesterday/today) commits to the development branch of kbin that look like they address the issues that fedia has been experiencing. I moved fedia to the development branch and reloaded some things, and so far, no error 500's.
But, caveat emptor, we are on the development branch of early-in-its-lifecycle open source software.
My understanding is that when an instance subscribes to a magazine or community, the instance is effectively subscribing to updates and so the local cached copy is kept up to date. That, of course, breaks down when there are issues with federation. I do wonder: are you seeing this with all non-local magazines?
It seems that there is still some problem with certain lemmy instances. For example, lemmy.ml actively blocks kbin based instances (like fedia) and so I don’t think the magazines (lemmy calls the communities) coming from that instance are being updated.
I'm not seeing this with all non-local mags, but I'm def seeing it with all non-local mags that I'm subscribed to. I first thought it was a problem with subscription and tried desubbing and subbing again, but it doesn't seem to have an effect.
It's not a very breaking problem when it comes to threads, but it is when it comes to comments, because sometimes even if a thread (post) is mirrored, it's incomplete and thus I cant participate in a specific comment tree.