On Bonvoy FB page today--and I tried to make a booking in Dec/Jan. Unable.
Thanks to this group, I contacted Bonvoy today and confirmed that the Ritz Carlton Cancun has been sold to another hotel chain (they wouldn't tell me), and they are no longer accepting new reservations under bonvoy. My points reservation in November would not have been honored, although they said they would honor the reservation itself in cash (not quoted). The front desk of the hotel was confused why I hadn't been contacted yet.
I backed out of the RC reservation and switched to the JW.
Thanks to everyone here, for all your posts. They all help!