Weird font rendering in Chrome on the SWR site

Sorry about the confusing nature of the images - I'll explain what's going on:

I clicked a link to swr.vercel.app on the facebook react documentation and noticed that the subtitle font was different to a duplicate of the page I opened the other day.

OK, weird, I refreshed the old page that was already open and the font remained the same.

OK? I disabled ad-blocking because some of the tracking scripts were off but still the same issue...

I noticed in the DOM panel that some of the scripts down the bottom were in different orders so there's clearly something weird going on.

When I opened it in Incognito, it was showing the latest version.

When I duplicated the old version I had open however, even the duplicate had the same alternate font.

Only when loading the page fresh by typing out the URL did I get the latest version of the page.

I even tried hard-refreshing with dev-tools open.

What's this weirdness?