Why does show the first page items, then show blinking dots, then show the items again?

[I originally noticed this issue with both react-hn and preact-hn. Since I understand that the preact version is based on the react version, I posted this issue at https://github.com/insin/react-hn/issues/94 first (9 days ago now). But I have seen no response there. I thought it might therefore be useful to also post it here. Maybe it can be fixed for the preact version even if it remains in the react one.]

On my macOS machine, in Safari or Google Chrome, preact-hn very quickly shows the full front page of Hacker News, with all its items, but then it shows blinking dots, and then shows the items again.

I assume the quick display is because of SSR. But why can't those items stay on the screen until everything is loaded? It looks terrible and slow the way it works now, but could appear very snappy if the SSR-rendered page just seemed to stay on the screen.