Our Git and Mercurial HTTPS services had sporadic issues between roughly 02:00 and 03:00 UTC on 15 October 2015. During that time, users attempting to push, pull, or clone repos over HTTPS may have experienced very slow response times or timeouts. Pushes and pulls over SSH were unaffected, as were the GUI, the API, and source downloads.
Upon investigation, we tracked the problem to a database server that handles authentication queries for the affected services. Once we failed those queries over to another server, normal service was restored.