I just discovered this: How to install letsencrypt certificate on qnap with virtual hosts - #2 by schoen
I do not have the default port 80 redirected to my NAS. The NAS doesn't accept connections from this port, either. Could it be that when the NAS tried to auto-renew the certificate, it couldn't due the the port not being port 80? Should I change both in the router and in the NAS, in the future? Or is there another way?
Could this be the culprit of my problems?