It seems to be a problem with the certificate. The http version is good.
It's kind of funny the way I noticed this: I consume the RSS feed for the Paul Graham's essays he has setup in there (https://www.aaronsw.com/2002/feeds/pgessays.rss). When I check my RSS reader for problematic feeds, sure enough I got an error for that feed.
Anyway, is anyone responsible for that site?