If the WHM page shows random characters (as opposed to legible words), it means your php.ini file may be misconfigured or have serious errors within. One way to confirm it is to follow these steps:
1) Rename /usr/local/lib/php.ini using this command: mv /usr/local/lib/php.ini /usr/local/lib/php.ini.unixy
2) service httpd restart
3) Navigateto WHM -> cPanel Varnish and confirm the random characters are no longer appearing
Once done, you may want to restore the renamed php.ini file as such:
1) mv /usr/local/lib/php.ini.unixy /usr/local/lib/php.ini
2) service httpd restart
Sometimes these random characters are due to a misconfiguration in the compression mode as configured in PHP (output_handler = ob_gzhandler). Turn compression off and try again (zlib.output_compression = Off)