Ref T13168. I'm not sure how this worked before, but I ran into this issue on my new laptop.
SiteSource accesses PhabrictatorEnv::getEnvConfig('phabricator.base-uri') when local, which may poison the cache and lock the value since we don't later discard the cache.
Specifically, when I access http://locala.phacility.com, I was getting an error like "You made a request for locala.phacility.com, but no configured site can serve this request.". This was because the base-uri was being incorrectly frozen as "local.phacility.com". The expectation is that it will match, so the standard PlatformSite will serve the request.