There has been an issue identified in WHMCS version 7.6.0 whereby, with the eNom registrar module activated, the nameserver names on the admin side client's domain details page appeared blank.
WHMCS have released a Hotfix for this which is available from https://whmcs.community/files/file/94-module-6830-enom-module-is-not-showing-nameservers-in-the-admin-area/
