Https://Lemmy.ml is extremely slow and buggy, is that common among instances?

it's running the 0.18.0 version which has some SQL problems that were fixed in recent 0.18.1 rc's

(unless the devs here are using a custom build)

It's run by the people that are making Lemmy. They're very busy improving the code, which we already benefit from on our server, but I understand they don't also have the time to update lemmy.ml with every change in code. I think a lot will improve as soon as 0.18.1 is released and am sure they will update lemmy.ml as well.

Slow, no, but there’s definitely some bugs and weird little quirks. We’re not even at a version 1 release yet.