According to this article 494,350 people took the listening test. 222 retook it because of mechanical trouble. That is also 180 out of 783 test sites that had retakers. That means that a test taker has a 0.045% chance of getting a bad player. 22% of the test sites had to give a retake for the same reason. Major success, I'd say!
センター試験 英語リスニング、２４９人が再試験（毎日新聞） - Yahoo!ニュース