I've had the lets encrypt renew script fail silently once. I found out when we started getting warnings like this. Turned out to be a mis-configured server tha

I've had the lets encrypt renew script fail silently once. I found out when we started getting warnings like this. Turned out to be a mis-configured server that had broken some months before. Our fault of course. But it still happened. Probably a good idea to monitor your certificate expiration. You don't want to cut it too close.