I noticed that the certificate for one of my sites was broken, simply being out of date. I checked on the server it was on and tried running the `acme.sh --cron` command to manually trigger an attempt to renew. Usually if something is broken, this process will fail with an error, however this time nothing did. I next tried to do `pkill -HUP nginx` to trigger a reload of config for the nginx process, and it fixed the issue. My guess is nginx does not reload the certificate unless explicitly told to do so. This is probably because I'm using the "webroot" configuration with [[acme.sh]], which does nothing special with nginx to trigger a reload.