Google itself confirmed the glitch and its results, saying that less than 0.08% of the Google Mail user base has been affected. The issues has still not been resolved and some users still can't access their accounts.
Google confirms that "users may be temporarily unable to sign in while we repair their accounts", but doesn't say if the content will be restored, too.
Users are understandably upset. As the number of affected accounts seems to be around 150,000, I expect Google isn't happy, either.
Was it a glitch, a bug, a human error? The company's team is investigating the issue, but there are still no concrete answers as they continue to push out uninformative updates on the situation every two hours.