For the last few days, the server on which this website (and many others I run!) started acting strangely. Every so often, nginx would stop working and I'd have to restart the service manually. I had restarted nginx two or three times over the last few days so I knew something wasn't right. I spent some time this afternoon figuring out what was wrong. I found an issue with certbot renewals and nginx that, when resolved, fixed the errors I found in nginx and the /var/log/syslog file on my computer.