It happens, although pretty rarely, for updates of WHM and cPanel to fail. Then you can access any of their pages and you are prompted to reload the page as if this would fix it.

Solution for me was just to run the following command as root in a SSH session on the server:

My output looked like this:

[2017-04-15 22:22:07 +0300]
[2017-04-15 22:22:07 +0300] Problems were detected with cPanel-provided files which are RPM controlled.
[2017-04-15 22:22:07 +0300] If you did not make these changes intentionally, you can correct them by running:
[2017-04-15 22:22:07 +0300]
[2017-04-15 22:22:07 +0300] > /usr/local/cpanel/scripts/check_cpanel_rpms –fix
[2017-04-15 22:22:07 +0300] The following RPMs are missing from your system:
[2017-04-15 22:22:07 +0300] cpanel-perl-524-Cpanel-Optimizer-0.2-1.cp1162
^C
orepair fix_duplicate_cpanel_rpmsel/scripts/check_cpanel_rpms –fix /scripts/aut
[2017-04-15 22:27:38 +0300]
[2017-04-15 22:27:38 +0300] Problems were detected with cPanel-provided files which are RPM controlled.
[2017-04-15 22:27:38 +0300] If you did not make these changes intentionally, you can correct them by running:
[2017-04-15 22:27:38 +0300]
[2017-04-15 22:27:38 +0300] > /usr/local/cpanel/scripts/check_cpanel_rpms –fix
[2017-04-15 22:27:38 +0300] The following RPMs are missing from your system:
[2017-04-15 22:27:38 +0300] cpanel-perl-524-Cpanel-Optimizer-0.2-1.cp1162
[2017-04-15 22:34:11 +0300] Removing 0 broken rpms:
[2017-04-15 22:34:11 +0300] rpm: no packages given for erase
[2017-04-15 22:34:18 +0300] Downloading http://httpupdate.cpanel.net/RPM/11.62/centos/6/x86_64/rpm.sha512
[2017-04-15 22:34:19 +0300] Successfully verified signature for cpanel (key types: release).
[2017-04-15 22:34:19 +0300] Downloading http://httpupdate.cpanel.net/RPM/11.62/centos/6/x86_64/cpanel-perl-524-Cpanel-Optimizer-0.2-1.cp1162.x86_64.rpm
[2017-04-15 22:34:20 +0300] Disabling service monitoring.
[2017-04-15 22:34:42 +0300] Hooks system enabled.
[2017-04-15 22:34:42 +0300] Checking for and running RPM::Versions ‘pre’ hooks for any RPMs about to be installed
[2017-04-15 22:34:42 +0300] All required ‘pre’ hooks have been run
[2017-04-15 22:34:43 +0300] No RPMS need to be uninstalled
[2017-04-15 22:34:43 +0300] Installing new rpms: cpanel-perl-524-Cpanel-Optimizer-0.2-1.cp1162.x86_64.rpm
[2017-04-15 22:34:44 +0300] Preparing packages for installation…
[2017-04-15 22:34:44 +0300] cpanel-perl-524-Cpanel-Optimizer-0.2-1.cp1162
[2017-04-15 22:34:45 +0300] Hooks system enabled.
[2017-04-15 22:34:45 +0300] Checking for and running RPM::Versions ‘post’ hooks for any RPMs about to be installed
[2017-04-15 22:34:45 +0300] All required ‘post’ hooks have been run
[2017-04-15 22:34:45 +0300] Restoring service monitoring.

Obviously, you’ll have to wait some time before the process ends, so don’t be too hasty at calling it hanging.

If this doesn’t help, you should have a look at this support thread.