For context, they had a service disruption a week ago due to preparations for IPv6 support on GitHub.com: https://www.githubstatus.com/incidents/5y8b8lsqbbyq ht

For context, they had a service disruption a week ago due to preparations for IPv6 support on GitHub.com: https://www.githubstatus.com/incidents/5y8b8lsqbbyq https://www.githubstatus.com/incidents/5y8b8lsqbbyq. I don't think they mentioned this anywhere else. Copied from that report: This incident was the result of an infrastructure change that was made to our load balancers to prepare us for IPv6 enablement of GitHub.com. This change was deployed to a subset of our global edge sites. The change had the unintended consequence of causing IPv4 addresses to start being passed as an IPv4-mapped IPv6-compatible address to our IP Allow List functionality. For example 10.1.2.3 became ::ffff:10.1.2.3. While our IP Allow List functionality was developed with IPv6 in mind, it wasn't developed to handle these mapped addresses, and hence started blocking requests as it deemed these to be not in the defined list of allowed addresses. Request error rates peaked at 0.23% of all requests.