Version 9.701-6 in HA Cluster mode. Seems that LetsEncrypt are having issues getting the config file from our firewall, or WAF is interfering with this process..
It looks like upstream device or ISP is blocking UTM's access to Let's Encrypt servers. Let's Encrypt service requires to connect to server and verify the domain ownership before issuing or renewing a Certificate.
Early the following morning our LetsEncrypt certs renewed of their own accord. Must have been to many tries for one day...
Thanks for the update. Good to know that it has been resolved.
You'll be shown a different error if you have tried for more than the limit. Please refer to this article Sophos UTM: Understanding status code 429 error in letsencrypt.log