I suspect the instance you are connected to is returning the 503 due to overload.
It’s World, which makes sense at it’s being slow.
I really need to join a different instance.
I joined a smaller instance and I stopped getting errors in my client. I think the huge ones are entering territory where the software has never been pushed before. They are groaning under the load.
A 5XX error indicates the error is not on the client (so this app) side, but an issue with the server. So there is really nothing you or the app dev can do, the lemmy instance admins need to fix it.
I would say there is a UI error: failing to upvote or loading the next page shouldn’t show a full screen error message and lose the state.
It’ll be ironic if this comment doesn’t post… I’ve made a couple comments on the app but they just never show up?
Edit: hmm… This one worked. My first ever comment on Lemmy, wooo. Not sure what happened with the others lol