I got an email that my certificates were going to expire.
Given they are set to auto-renew, this seemed odd.
I logged in to the server and some errors indeed in ~/var/log/letsencrypt/letsencrypt.log
Along the lines of
Detail: 126.96.36.199: Fetching http://commonplace.doubleloop.net/.well-known/acme-challenge/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx: Timeout during connect (likely firewall problem)
And indeed it was a firewall problem. I did not have port 80 open, just 443 and some others.
ufw allow http certbot -q renew
Weird that this just manifested though. What changed?