No, I don't think this is a server problem, it's a UI problem: If there is no mistake, there is no visible feedback. Which makes it hard to tell the difference between being an awesome writer and seeing a broken website.

I've just tried it with:

I tried it on some decent-looking HN comments. I am impressed that every "problem" it has found has been plausible, but disappointed that all have been wrong. This checker has one hell of a false positive rate.

No errors / suggestions. I didn't get any feedback that the text has been analyzed and is ok.

(I tried it with the original text and got some suggestions. It's working.)