I don't want to give false information, but on fedia the majority of 500 pages seemed to stem from the image media cache causing issues (our instance admin detailed the issue here). People were able to mitigate it by disabling images everywhere they could, but one place they can't be disabled is the user avatars on the notification page. I could be wrong, but it's my belief it's those images causing the 500s, and that pushed me to add https://codeberg.org/Kbin/kbin-core/issues/1039 in hopes that if it was possible to disable them the 500s would stop. All this could be wrong though, maybe it's something else like deleted messages or anything else, or maybe there's a better way to solve issues with cached images