If you examine the /etc/letsencrypt/renewal/openbsd-network.org.conf file, it will say which document root directory or directories Certbot is configured to use. Are they correct? (/foo/ means Certbot will place the files in /foo/.well-known/acme-challenge/.)
What do the web server error logs show?
What’s changed since the certificates were created or the last time they were renewed? Is the IP address in the DNS records still correct? Have the websites been changed to use different document roots?