During an update on the edge layer to replace the development environments' TLS certificates, a kernel bug prevented the restart. The issue caused the whole EU region to go down on November 15, 2018 for about 15 minutes between 15:58 and 16:13 UTC. All sites hosted on the region were down during that time.
Engineers quickly manually rebooted the 3 gateways which brought the service back online. Kernel versions are in the progress of being updated on all regions to ensure that this does not recur.