As @BartButenaers mentions above, don't forget about the httpsRefreshInterval which has been introduced into node-RED since v1.1.0.
A bit of background....
By default, node-RED reads in the SSL certificates only when node-RED starts, so even though you have renewed your certificates with certbot. Node-RED will not load them until it has been restarted.
To deal with this, if you use httpsRefreshInterval in your settings.js file, then the certificates will be reloaded into the running system automatically, avoiding the need to restart the system.
