@TeamYouTube
I just discovered that my channel monetization is ineligible due to 'duplication' but I never received any email! I had to check the problem after realizing that I am not receiving any revenue anymore + my account is in a good standing. I believe it's a mistake!
The best place to check is your Monetization page in Creator Studio: https://goo.gl/jbWMVx . From there, you’ll see an explanation with links to relevant resources. You’ll also see the option to reapply from that page in 30 days!