Demoting 2016 server problems

I am trying to demote a Windows 2016 server and am running into errors. I am using a Domain Admin account. The error that comes up is that the domain cannot be reached which is strange, considering that all DCs are reachable from this server. It is not running a GC and the DNS server on it has been removed. This is a relatively small domain with only three DCs. We are demoting this one so that we can add a new Windows 2022 DC and eventually 2025 DCs.

We have two sites: Office and Datacenter. There are two DCs at Office and one at Datacenter. Going forward we will be removing one of the office DCs and adding a second one at Datacenter. Let's call these servers:
Server Alpha, 172.16.1.1, Datacenter 
Server Bravo, 172.17.1.1, Office (this is the server to be removed)
Server Charlie, 172.17.1.2, Office

When I run the command:    dcdiag /test:dns /DnsRecordRegistration on each of these servers I get the following:

Server Alpha: Success, no errors 
Server Bravo: Success, no errors
Server Charlie: DNS error, points to very old IP (172.20.1.1) that Server Bravo used to have when it was at an older, DR datacenter. The error is: "PTR record query for the 1.0.0.127.in-addr.arpa. failed on the DNS server 172.20.1.1"

We do still have the reverse DNS zone for that subnet however neither of the other two servers have this problem. Also I cannot find any other entries for that IP address anywhere.

What am I missing?