Sql servers are using Kerberros and NTLM Authentication Lately I have been facing failed connection errors mainly due to servers using NTLM Authentication. In our environment the servers have a combination of ntlm and kerberoos. My question is If i ask my Domain admin to manually register all the service accounts to use the kerberoos instead of ntlm authentication will there be any problem or any performance issues that might arise ?
Kerberos authentication should be faster and it is definitely more secure, so if you are at all concerned about security it should be enabled.  The only issue that I can think of that might occur is if the Service Principal Names (SPNs) incorrect, then logins will fail.  Accordingly, if you are adding SPNs to get it set up, I would recommend having the SETSPN commands ready so you can quickly will back out the changes that were made.  


Add new SPNs
Test client / application connections (restart applications that connect to force new logins)
Remove SPNs if tests fail and investigate


Ref: What Is Kerberos Authentication?