DCDIAG errors -failing advertising and more tests - appear to be due to flatname issues

I'm running "DCDIAG /Q /E " between my two domain controllers, and one of them is getting errors.  I'm running as admin of course!

The first DC is sitting on subnet1, and is called ACMEDC1.

The second DC is sitting on subnet2, and is called ACMEDC2.

When I run on ACMEDC2, there are no errors.

When I run on ACMEDC1, there are some errors:

         Fatal Error:DsGetDcName (ACMEDC2) call failed, error 1722

         The Locator could not find the server.

         ......................... ACMEDC2 failed test Advertising

         [ACMEDC2] An net use or LsaPolicy operation failed with error 64,

         The specified network name is no longer available..

         ......................... ACMEDC2 failed test SysVolCheck

         Could not open pipe with [ACMEDC2]:failed with 64:

         The specified network name is no longer available.

         Could not get NetBIOSDomainName

         Failed can not test for HOST SPN

         Failed can not test for HOST SPN

         [ACMEDC2] An net use or LsaPolicy operation failed with error 64,

         The specified network name is no longer available..

         ......................... ACMEDC2 failed test NetLogons

I can do a lookup of ACMEDC2 with nbtstat - it will resolve to an IP address and then it appears in the cache (so "nbtstat -a ACMEDC2" and "nbtstat -c" work.

However, from ACMEDC1, I have also noticed that I cannot connect to any SMB shares on SOME servers when using the netbios name.  There doesn't seem to be any rhyme or reason - server version, subnet.

For example, from ACMEDC1:

I can connect to \\ACMESRV1\fileshare 

(or any share)

If I try to connect to ACMEDC2:

\\ACMEDC2.ACME.LOCAL\FILESHARE

works

\\(IP ADDRESS)\FILESHARE

works

But:

\\ACMEDC2\FILESHARE

fails with the error "Windows can't find '\\ACMEDC2\FILESHARE'.  Check the spelling and try again."

I can connect to SMB successfully with PowerShell too.  nbtstat -RR (or -R) do not resolve the issue either.

So I think that whatever is causing the issue with the SMB connection to the flatname is causing the same issues in DCDIAG.  I am not seeing any problems with any other AD services - replication works perfectly, and ACMEDC2 is having no such issues in SMB or DCDIAG.