Jenkins Resource root URL - serves only static file on the domain

Jenkins 2.445 
We have many jobs that runs userContent at the end to display the reports. userContent in JENKINS_HOME has css,html and js file. We also setup system property to cross-site scripting XSS to display the reports. All the reports working perfectly. 
Now we dont want to allow the XSS remove the system property (CSP) but want to make use of Resource root URL. There in manage jenkins -> system -> Resource Root URL configured new dns URL with following condition stated by jenkins.

* The resource root URL must be a valid alternative choice for the Jenkins URL for requests to be processed correctly.
* The Jenkins URL must be set and it must be different from this resource root URL (in fact, a different host name is required).

Jenkins restarted, userContent have all permissions. when accessing jenkins userContent with actual hostname(https://actualjenkin_hostname/userContent) all the files are getting displayed. Whereas with new Resource root URL (https://newdns_hostname/userContent) to access userContent it gives error
Jenkins serves only static files on this domain, 404 error