*** I HOPE THIS HELPS OTHERS ***
In October 2019, I received a notification from Comcast (Bay Area) to upgrade to a new cable modem that supports DOCSIS 3.1 to take advantage of higher Internet speeds. I upgraded to the MOTOROLA MB8600 in mid-November 2019. In December 2019, I randomly (no notification from Comcast) saw my Monthly Data Usage exploded past 1 TB - we're consistently under <=200 GB/month. Our Internet usage pattern did not change nor did we add any new devices and/or services. Without an explanation from Comcast, I reverted back to my old cable modem. Since then we have seen our Monthly Data Usage back to normal. I've concluded this to be a bug with Comcast and/or the cable modem software.
Here's an article on this, but doesn't look to be resolved: https://arstechnica.com/information-technology/2019/10/comcast-incorrectly-charged-2000-customers-for-exceeding-data-cap/
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