I use LetsEncrypt to provide an SSL certificate at www.crispygeek.com, which runs off UbuntunServer.
Every 2-3 days, I receive the error “invalid webserver configuration”. I am able to resolve the issue temporarily by using the commandline tools to reinstall the certificate, however 2-3 days later the issue returns. This only started 2-3 weeks ago after working fine for nearly a year.
My main inkling that its related to SSL is when I reinstall the certificate, it works fot a period of time, so that to me suggests it is somewhat related.