Ah, I needed to update the CNAME for the #ConfigMgr CMG upgrade. Right! Ok, now in place. Now we'll see if remote clients can start checking in with the site server.
#DNS #SCCM #CloudManagementGateway
https://learn.microsoft.com/en-us/mem/configmgr/core/clients/manage/cmg/modify-cloud-management-gateway#update-or-create-a-dns-cname