That link shows some more info, including a link to:
Please read that thread 
Note: this change has been coming for over many months (if not years) now.. Also, if you're affected by this brown-out, you're probably not renewing soon enough: Let's Encrypt recommends renewing after 60 days, so you have a 30 days "window" if anything goes wrong. This brown out is only 48 hours long. No offence, but if your site is offline for thousands of users due to a brown out of 1/15th of the recommended renewal window, you might have to rethink your renewal process.