Sorry, but I can hardly see that you at least tried to search by yourself for a solution.
The search function will show you also threads in english like Kinit broken in univention/ucs-master-amd64:4.2-1 after initial config and restart which will give additional information.
In short: Something is wrong with your kerberos setup. You have to fix it before you can try to fix the DNS stuff.
In case you dont understand details feel free to ask.
Best Regards,
Dirk