Remote connection to the instance with window account and NTLM is failing I have the windows server with 4 SQL server 2012 instances
This is the test server. SPNs are not registered for any of those instances.

I can successfully connect remotely to 3 of those instances using my windows account, however for one of it I got following error:
The target principal name is incorrect.  Cannot generate SSPI context.

SQL Server login connections are working ok.

We've tried registering/de-registering the SPNs, also created new MSA account for that instance.

From what I've read - when the SPNs are not registered - the NTLM should be used. NTLM is working correctly for remote SQL Server logins.

What else can be checked? Is there any other option forcing this instance to try to use Kerberos connection?

This is the SQL Server 2012 patched to the 11.0.7462.6.
This can be caused by one of three things:


The service account has an expired password. 
The service account has been locked. 
The service account does not have permission to create
an SPN.