fwiw I’ve tried running “ss -tulpn | grep lighttpd” in a separate terminal while letsencrypt states that it’s listening for the https request… and it never appears to open port 443 to ipv6 traffic.
EDIT: It seems to be the same problem shown here: https://dietpi.com/forum/t/lets-encrypt-for-ipv6-only-websites/4334/1
I manually edited the ssl conf in /etc/lighttpd/conf-enabled/ to “[::]:443” similar to the post above and restarted. It opened port 443. I ran letsencrypt, and it errored out at the end. I ran it again and it said the certificate already existed and was current for a long time. I chose not to overwrite… and my website is now accessible over ipv6. Looks like it actually succeeded in creating the certificate the first time despite the error.
If I can do anything to help fix this bug, please let me know.