It appears likely that this was a test procedure failure rather than a hardware failure. Which brings up the question, why were they doing it at 2AM? Either they were using night crew who are presumably not their A staff or they were using highly fatigued day crew.

Edit: everybody is taking this as an attack on night crew. It was poorly worded -- I believe the latter is more likely, since Elon expects his employees to work 80-100 hours a week. https://www.businessinsider.com/elon-musk-says-80-hours-per-...