In a blog post, Google stated that its automatic security detects and prevents access to files that might contain viruses, malware or 'other abusive content.' The bug caused Docs and Drive to misinterpret the signals from these systems, which resulted in erroneously marking particular files as violating TOS. While it's as much a mea culpa as you'll get from the internet giant, getting randomly locked out of your own documents was a wake-up call for some users who realized how much they depended on Google to access their cloud-based files -- access that can be revoked or shut off by bugs or intention.

Yep. I can't trust @googledocs, any more. If this was the day before a grant submission, it could literally cost us £100k+ — Leighton Pritchard (@widdowquinn) October 31, 2017

In the post, Google reassured users that it would strive to keep files secure and safe: "We apologize to our users for any inconvenience this incident caused and remain committed to offering high-quality systems that keep their content safe while fully securing their files."