When you get this message:

May 21 00:13:31 nfs03.nix.mds.xyz [sssd[krb5_child[1822]]][1822]: Key table entry not found

followed by:

[[sssd[krb5_child[1752]]]] [k5c_setup_fast] (0x0020): 2628: [-1765328203][Key table entry not found]

or similar, dig into the logs further to see this:

(Mon May 21 00:13:33 2018) [[sssd[krb5_child[1824]]]] [find_principal_in_keytab] (0x0400): No principal matching host/nfs02.nix.mds.xyz@NIX.MDS.XYZ found in keytab.
(Mon May 21 00:13:33 2018) [[sssd[krb5_child[1824]]]] [check_fast_ccache] (0x0080): find_principal_in_keytab failed for principal host/nfs02.nix.mds.xyz@NIX.MDS.XYZ.
[root@nfs03 sssd]#

Then check your /etc/krb5.conf file:

[root@nfs03 etc]# grep -Ei nfs02 *
krb5.conf:  nfs02.nix.mds.xyz = NIX.MDS.XYZ

And also here:

[root@nfs03 etc]# grep -EiR nfs02 * 2>/dev/null
sssd/sssd.conf:ipa_hostname = nfs02.nix.mds.xyz
sssd/sssd.conf-new:ipa_hostname = nfs02.nix.mds.xyz
[root@nfs03 etc]#

And change accordingly.  The issue resulted from copying the same files from another host, nfs02.

Cheers,
TK