I had the same issue. Comcast tech couldn't find a way to activate MoCA, even after consulting with his supervisor. I was told to take it up with Arris as it's customer owned equipment. Arris support told me MoCA was DISABLED on that device because it interferes with Comcast's X1 equipment. No help from Arris.
Almost by accident, I discovered a hidden page in the user interface where MoCA can be enabled. After logging into the modem, the page can be accessed at 10.0.0.1/moca.php . I've had it up and running for over 2 days now with no problems.
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