It's probably not directly related to these changes if you're only doing it Saturday and it's only on old.lemmy.com, but if you're looking into load problems, might be indirectly relevant. In the past...I think two days, using the standard Lemmy Web UI, I've seen a high rate of the server returning a page just reading:

Error!

There was an error on the server. Try refreshing your browser. If that doesn't work, come back at a later time. If the problem persists, you can seek help in the Lemmy support community or Lemmy Matrix room.

Sometimes, but not always, the above error text is also followed by:

The server returned this error: Error. This may be useful for admins and developers to diagnose and fix the error

This has not, as far as I can tell, shown up when trying to view lists of posts (like, when I view all subscribed posts) but it does show up when trying to view the page for a post. It appears to affect all posts for me, not just specific ones.

I initially thought that its just that the post had been deleted, but I could view said posts fine on the original, remote instance.

One such example that I just hit, tried to load a number of times unsuccessfully:

https://lemmy.today/post/57605044

Which has, as a remote post:

https://nord.pub/c/games@lemmy.world/p/326761/is-routine-worth-playing

I reloaded five or six times, and eventually it came up locally on lemmy.today.

When it happens, it seems to affect all of the post pages that I try to load.

When I see this, the error page comes up pretty quickly, maybe in a second, so it's not some (long) timeout. Maybe hitting some limit on concurrent database queries or something like that?

tries loading page again

And now that post is back to showing an error. Also, I saw it without doing a cache-invalidating reload on Firefox (shift-reload rather than a normal reload), so whatever the server is trying to generate, and failing, it's not driven by the server trying to respond to something that my browser will have cached.

When the problem is happening, the same problem also shows up when I try to view my user profile page (so doesn't as best I can tell, affect lists of posts, either "all subscribed" or viewing posts in a community, but does affect individual post pages and does affect user profile pages).