A misconfiguration on our proxy servers will have resulted in the sites that usually see the ERR_HIGH_TRAFFIC warning being mostly unavailable from 8AM until about 8:30PM. Users will likely have found that accesses to these sites timed out with an ERR_READ_TIMEOUT error.
The error was introduced by an improvement implemented as result of our recent experiments. This has now been corrected, and normal access has been restored. The new configuration is now operating correctly.
This problem was obscured by the concurrent Internet outages. The only two problematic sites reported to us, facebook.com and youtube.com, both suffered from separate DNS-related problems that had identical symptoms and that were directly attributable to the outages. These problems were beyond our control and only resolved themselves about an hour after each outage ended. Thus it was only once our Internet access was fully restored and the DNS problems had completely resolved themselves that the true extent of the initial problem became apparent.
Our apologies for the inconvenience this may have caused.