I am well aware of the rate limits, but I had actually found another potential problem. If the site already has a https redirect in place in the Rewrite Rules/.htaccess file and there is no valid SSL certificate, then it will be inaccessible including for the Let’s Encrypt challenge. Here are the details:
/home/office.techandtiny.com/public_html -d office.techandtiny.com
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator webroot, Installer None
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for office.techandtiny.com
Using the webroot path /home/office.techandtiny.com/public_html for all unmatched domains.
Waiting for verification...
Cleaning up challenges
Failed authorization procedure. office.techandtiny.com (http-01): urn:acme:error:unauthorized :: The client lacks sufficient authorization :: Invalid response from http://office.techandtiny.com/.well-known/acme-challenge/yF5zytN0pisE-NTOn3BHxc4R5YDfsgxUhYrrSobc8rw: "\
\
404 Not Found\\r\
\
<body style=\"color: #444; margin:0;font:"
\
404
Not Found\\r\
\
<body style=\"color: #444;
margin:0;font:"
To fix these errors, please make sure that your domain name was
entered correctly and the DNS A/AAAA record(s) for that domain
contain(s) the right IP address.
A possible workaround could be temporarily disabling the .htaccess file or Rewrite Rules if a first attempt is detected as failed and then reattempting a second time with the .htaccess with disabled. Just some food for thought.