Resolved - It turns out to be an caching issue with the SSL certificates in the backend, causing hosting 4 to have an older certificate than hosting 5. Currently the IPv4 traffic is routed through an DigitalOcean floating IP which sends traffic to hosting 5 and redirecting to hosting 4 when there’s an issue. Since DigitalOcean doesn’t have a floating IP feature for IPv6 and hosting 5 currently isn’t in an IPv6 region those requests are allways served by hosting 4. The certificate on hosting 4 was up to date but HAProxy wasn’t reloaded when the certificates were refreshed causing it to serve pages on IPv6 with an old certificate.
Investigating - Reports are coming in that for some users the certificate has expired and for some users everything works fine.