A bug in some Google Home speakers is causing them to download large amounts of data, up to 3TB, for no clear reason. https://www.pcmag.com/news/check-your-google-home-speaker-new-bug-downloads-up-to-3tb-of-data-a-month
PCMAGCheck Your Google Home Speaker: New Bug Downloads Up to 3TB of Data a MonthA fix is rolling out now, but the issue may have affected your speakers since early October.