Earlier quoted context omitted.
That link is for actual DMCA notices. With the Content ID take-downs, Google never actually receives a DMCA request. The music company (etc.) politely asks YouTube to take down the video, and YouTube complies out of the goodness of its heart. (Well, and a bunch of contracts that give some sort of quid pro quo for the arrangement between YouTube and these companies.) It looks like these are all Content ID takedowns (w…
All of which makes Google liable for theft. They created the system, they run the system, they transfer the money. It's all facilitating copyfraud. Just because Google agrees to host the content doesn't mean that they are incapable of being able to be sued for their intentional actions.
You're choosing to let YouTube publicly host the video until further notice, and in exchange they agree to pay you whatever cut of ad revenue they deem appropriate. There's no question that under the terms you agree to, they can demonetize your videos at will. And if they also see fit to start paying somebody else when your videos get played, that's not something you have legal standing to complain about.
What it probably is, is fraud on the part of whoever's falsely claiming to Google that they have a copyright interest.