I did a docker logs -f app and saw errors about LETSENCRYPT_ACCOUNT_EMAIL being invalid (it appears to have the value “OFF” in your earlier versions of the file). I changed it to your email address, rebuilt, and it’s working now.
I’m not sure if something changed to require that it be a valid email (It should be removed since let’s encrypt no longer will use that address to notify you of a problem.
I don’t have time now to check the commits to see if something’s changed about this, but I don’t remember seeing anything.