Thanks for the information. Users of Certify The Web are starting to see this issue now (some of our DNS providers have configurable propagation delay but regrettably not all, that will obviously get fixed).
I also wondered what the trigger for the email ‘Action required: New feature and your Let’s Encrypt integration’ is? Does it happen as soon as you try to renew and hit a validation error? I’m seeing a spike in support requests and just trying to understand why each person is seeing this. Is it possible some DNS providers actively block one of the IP blocks Let’s Encrypt is using?