Your certificate (or certificates) for the names listed below will expire in 11 days (on 28 Oct 21 05:03 +0000). Please make sure to renew your certificate before then, or visitors to your web site will encounter errors.
We recommend renewing certificates automatically when they have a third of their total lifetime left. For Let's Encrypt's current 90-day certificates, that means renewing 30 days before expiration. See Integration Guide - Let's Encrypt for details.
Your site sits behind CloudFlare CDN.
CF will automatically maintain the client side certificate.
CF can also provide server side certificates and can even connect to your server via HTTP (NOT recommended).
As such, there is not much we can troubleshoot for you.
We can't even be sure you are still using the LE cert mentioned in the email.
CloudFlare CDN was introduced into the equation; and they now pretty much control the encryption.
To make sure your encryption will not be affected after that cert expires, you should review the CF CDN process and the choices made within their service.