When I upgraded macOS to Sierra last month, I started getting this error on a few websites (Lifehacker, Xkcd, etc). When I try to read anything on Lifehacker, I get a particularly odd version of this error which says "Safari can't verify the identity of the website Kinja.com" ...but my link is for lifehacker.com
As I said, when I first upgraded to Sierra, I got the error... but a restart seemed to clear it up and I didn't get the error again until today when I updated to 10.12.1 and a restart didn't fix it (which makes sense. I don't know why a restart fixed it last time).
How do I fix this?