After upgrading from 5.3.1 to 5.7.0 the Hue "Web Server Status" is "The Cloudera Manager Agent is not able to communicate with this role's web server".
Both of the servers that run Hue have the same error message in "/var/log/cloudera-scm-agent/cloudera-scm-agent.log"
GSSAPI Error: Unspecified GSS failure. Minor code may provide more information/Cannot determine realm for numeric host address
This message appears every minute
On the affected nodes can you check;
a. reverse/forward lookup the <host.fqdn> part of your princial ie: [HTTP|hue]/<host.fqdn>@REALM - as the Kerberos message indicate that it unable to "... determine the realm for the numeric [ip] host address".
b. in your <host.fqdn> the 'fqdn' part is correctly associated with a REALM in the [domain_realm]
c. in krb5.conf check if dns_lookup_realm is configured correctly 
The generated principals are listed in CM UI> Administration> Security> Kerberos Credentials.
or you can set krb5.conf according to this 
I should have added that the server that hosts hue is also utilized as a jump host for access to the Cloudera cluster for management and has kerberos enabled for access.
For the Cloudera cluster, kerberos is not enabled.