If you are getting this:

krb5_child.log:(Tue Mar  6 23:18:46 2018) [[sssd[krb5_child[3193]]]] [map_krb5_error] (0x0020): 1655: [-1765328340][Cannot find key for nfs/nfs01.nix.my.dom@NIX.my.dom kvno 6 in keytab]

Then you can resolve it by copying the old keytab file back (or removing the incorrect entries using ktutil).  In our case we had made a saved copy and readded the NFS principals to the keytab file.  You can list out the current principals in the keytab file using:

klist -kte /etc/krb5.keytab

This was followed up by readding missing keytab keys from the IPA server:

ipa-getkeytab -s idmipa01.nix.my.dom -p nfs/nfs-c01.nix.my.dom -k /etc/krb5.keytab
ipa-getkeytab -s idmipa01.nix.my.dom -p nfs/nfs01.nix.my.dom -k /etc/krb5.keytab

Alternately, create the keytab entries manually using ktutil above.

Cheers,
Tom