Only good knows, but maybe it was mining other SHA-256 coins, or in that time the farm was in the deployment/upgrade phase and what we seen was only a test run.
The only credible explanation IMO is that is something new, some new chip being deployed. Maybe s6 testing.
No that's not a credible explanation at all. Have you ever thought about possible issues with a big mining farm? Power outages, DDOS and whatnot?