I get the error KDC_ERR_S_PRINCIPAL_UNKNOWN when I try to authenticate to an Active Directory realm from an Ubuntu 22.04 machine joined to the domain, using Kerberos.
I have a Windows machine joined to the same domain and I have no issues with the Windows machine.
I'm also unable to nslookup the Ubuntu machine from the DC but I can ping it just fine.
Turns out the issue was with DNS. There was no A-record in the DNS for the Ubuntu clients. The AD-join process for Ubuntu described here doesn't seem to automatically add the record. Adding the A-record manually to the DNS fixed the issue.