On April 12, 2020 between 21:59 and 22:350 UTC a number of customer sites experienced a disruption in service. Our engineers were alerted and they identified an underlying issue with pantheon.io and pantheonsite.io domain names. Sites following our recommendation to use A/AAAA DNS records were unaffected. We have taken steps to ensure the failure does not recur. We also recommend that customers take action to update any domains still using CNAMEs and switch to A/AAAA records, your site dashboard will show “Update Recommended” in “Domains / HTTPS” if your site DNS config is still using CNAME.
For more information see: https://pantheon.io/docs/dns#why-does-my-domain-say-update-recommended
We sincerely apologize for the negative affects our customers experienced and will work to continue to earn your trust.