"Your certificate (or certificates) for the names listed below will expire in 9 days (on 17 Aug 21 15:58 +0000). Please make sure to renew your certificate before then, or visitors to your web site will encounter errors"
even though I have renewed the certificate and the Certificate Validity for the domain in the browser shows that it valid thru 10/27/21
Is there a known problem with the email notification system ?
No, there isn't as far as I'm aware of. Please read the entire expiry e-mail and the documentation about the expiry e-mails linked in the e-mail itself. There's almost certainly a very logical explanation why you're getting the e-mail.
I went through the entire email and the documentation and did not see anything relevant to my scenario.
As indicated earlier, I renewed my domains successfully (no error messages) and uploaded the updated certs to the website and the browser shows the correct expiry.
I am at a loss as to how to move forward but thank you for your response.
The certificate containing both hostnames has not been renewed, only the certificates containing the hostnames separately. Therefore, Let's Encrypt, as indicated by the documentation, justly warns you the certificate with that exact set of hostnames has not been renewed.
Firstly, thank you for this incredibly timely response on a weekend. Mind boggling !
Secondly, I am sorry that I did not remember nor do I realize the distinction between a request containing multiple hostnames and one containing a single. Now I do. Thank you.
I will make sure that going forward we will renew the certificates in a consistent manner.